diff --git a/data/gui.xml b/data/gui.xml
index 5d515dbc6..6bb608ba0 100644
--- a/data/gui.xml
+++ b/data/gui.xml
@@ -664,6 +664,9 @@
         <item command="LayerVisibility" text="&amp;Visible" />
         <separator />
         <item command="NewLayer" text="&amp;New Layer" />
+        <item command="NewLayer" text="New &amp;Group">
+          <param name="group" value="true" />
+	</item>
         <item command="RemoveLayer" text="&amp;Remove Layer" />
         <item command="BackgroundFromLayer" text="&amp;Background from Layer" />
         <item command="LayerFromBackground" text="&amp;Layer from Background" />
diff --git a/data/pref.xml b/data/pref.xml
index 49c5889ca..f2aaadb37 100644
--- a/data/pref.xml
+++ b/data/pref.xml
@@ -228,7 +228,7 @@
   <document>
     <section id="site">
       <option id="frame" type="doc::frame_t" default="doc::frame_t(0)" />
-      <option id="layer" type="doc::LayerIndex" />
+      <option id="layer" type="doc::layer_t" default="doc::layer_t(0)" />
     </section>
     <section id="tiled">
       <option id="mode" type="filters::TiledMode" default="filters::TiledMode::NONE" migrate="Tools.Tiled" />
diff --git a/data/skins/default/sheet.png b/data/skins/default/sheet.png
index bc0ab7ac1..603278200 100644
Binary files a/data/skins/default/sheet.png and b/data/skins/default/sheet.png differ
diff --git a/data/skins/default/skin.xml b/data/skins/default/skin.xml
index ce0f74400..ea08d2bc4 100644
--- a/data/skins/default/skin.xml
+++ b/data/skins/default/skin.xml
@@ -329,6 +329,10 @@
     <part id="timeline_continuous_active"       x="288" y="36" w="12" h="12" />
     <part id="timeline_discontinuous_normal"    x="276" y="48" w="12" h="12" />
     <part id="timeline_discontinuous_active"    x="288" y="48" w="12" h="12" />
+    <part id="timeline_closed_group_normal"     x="276" y="60" w="12" h="12" />
+    <part id="timeline_closed_group_active"     x="288" y="60" w="12" h="12" />
+    <part id="timeline_open_group_normal"       x="276" y="72" w="12" h="12" />
+    <part id="timeline_open_group_active"       x="288" y="72" w="12" h="12" />
     <part id="timeline_empty_frame_normal"      x="240" y="60" w="12" h="12" />
     <part id="timeline_empty_frame_active"      x="252" y="60" w="12" h="12" />
     <part id="timeline_keyframe_normal"         x="240" y="72" w="12" h="12" />
@@ -525,12 +529,18 @@
     <style id="timeline_open_eye:active">
       <icon part="timeline_open_eye_active" />
     </style>
+    <style id="timeline_open_eye:disabled">
+      <icon color="disabled" />
+    </style>
     <style id="timeline_closed_eye" base="timeline_box">
       <icon part="timeline_closed_eye_normal" align="center" valign="middle" />
     </style>
     <style id="timeline_closed_eye:active">
       <icon part="timeline_closed_eye_active" />
     </style>
+    <style id="timeline_closed_eye:disabled">
+      <icon color="disabled" />
+    </style>
 
     <!-- timeline_padlock -->
     <style id="timeline_open_padlock" base="timeline_box">
@@ -539,12 +549,18 @@
     <style id="timeline_open_padlock:active">
       <icon part="timeline_open_padlock_active" />
     </style>
+    <style id="timeline_open_padlock:disabled">
+      <icon color="disabled" />
+    </style>
     <style id="timeline_closed_padlock" base="timeline_box">
       <icon part="timeline_closed_padlock_normal" align="center" valign="middle" />
     </style>
     <style id="timeline_closed_padlock:active">
       <icon part="timeline_closed_padlock_active" />
     </style>
+    <style id="timeline_closed_padlock:disabled">
+      <icon color="disabled" />
+    </style>
 
     <!-- timeline_continuous -->
     <style id="timeline_continuous" base="timeline_box">
@@ -560,6 +576,20 @@
       <icon part="timeline_discontinuous_active" />
     </style>
 
+    <!-- timeline_group -->
+    <style id="timeline_closed_group" base="timeline_box">
+      <icon part="timeline_closed_group_normal" align="center" valign="middle" />
+    </style>
+    <style id="timeline_closed_group:active">
+      <icon part="timeline_closed_group_active" />
+    </style>
+    <style id="timeline_open_group" base="timeline_box">
+      <icon part="timeline_open_group_normal" align="center" valign="middle" />
+    </style>
+    <style id="timeline_open_group:active">
+      <icon part="timeline_open_group_active" />
+    </style>
+
     <!-- timeline_layer -->
     <style id="timeline_layer" base="timeline_box">
       <text align="left" valign="middle" padding-left="4" />
diff --git a/data/widgets/new_layer.xml b/data/widgets/new_layer.xml
index a98813d0c..91b5d21b6 100644
--- a/data/widgets/new_layer.xml
+++ b/data/widgets/new_layer.xml
@@ -1,32 +1,20 @@
 <!-- ASEPRITE -->
-<!-- Copyright (C) 2001-2013 by David Capello -->
+<!-- Copyright (C) 2001-2016 by David Capello -->
 <gui>
-<window text="New Image Layer" id="new_layer">
-  <box vertical="true">
-    <box horizontal="true">
-      <box vertical="true" homogeneous="true">
-        <label text="Name:" />
+  <window text="New Layer" id="new_layer">
+    <box vertical="true">
+      <box horizontal="true">
+	<box vertical="true" homogeneous="true">
+          <label text="Name:" />
+	</box>
+	<box vertical="true" homogeneous="true">
+          <entry maxsize="256" text="New Layer" id="name" magnet="true" />
+	</box>
       </box>
-      <box vertical="true" homogeneous="true">
-        <entry maxsize="256" text="New Layer" id="name" magnet="true" />
+      <box horizontal="true" homogeneous="true">
+	<button text="&amp;OK" closewindow="true" id="ok" magnet="true" />
+	<button text="&amp;Cancel" closewindow="true" />
       </box>
     </box>
-    <box horizontal="true" homogeneous="true">
-      <button text="&amp;OK" closewindow="true" id="ok" magnet="true" />
-      <button text="&amp;Cancel" closewindow="true" />
-    </box>
-  </box>
-</window>
-<window text="New Layer Set" id="new_layer_set">
-  <box vertical="true">
-    <box horizontal="true">
-      <label text="Name:" />
-      <entry maxsize="256" text="New Set" id="name" />
-    </box>
-    <box horizontal="true" homogeneous="true">
-      <button text="&amp;OK" closewindow="true" id="ok" magnet="true" />
-      <button text="&amp;Cancel" closewindow="true" />
-    </box>
-  </box>
-</window>
+  </window>
 </gui>
diff --git a/docs/files/ase.txt b/docs/files/ase.txt
index 03ac3003c..1d1b33b58 100644
--- a/docs/files/ase.txt
+++ b/docs/files/ase.txt
@@ -156,6 +156,7 @@ Layer Chunk (0x2004)
                   4 = Lock movement
                   8 = Background
                   16 = Prefer linked cels
+                  32 = The layer group should be displayed collapsed
   WORD          Layer type (0=normal (image) layer, 1=layer set)
   WORD          Layer child level (see NOTE.1)
   WORD          Default layer width in pixels (ignored)
diff --git a/src/app/CMakeLists.txt b/src/app/CMakeLists.txt
index cabb775fc..33bf8ffbb 100644
--- a/src/app/CMakeLists.txt
+++ b/src/app/CMakeLists.txt
@@ -230,7 +230,6 @@ add_library(app-lib
   commands/cmd_new_frame.cpp
   commands/cmd_new_frame_tag.cpp
   commands/cmd_new_layer.cpp
-  commands/cmd_new_layer_set.cpp
   commands/cmd_new_sprite_from_selection.cpp
   commands/cmd_onionskin.cpp
   commands/cmd_open_file.cpp
diff --git a/src/app/cli/cli_processor.cpp b/src/app/cli/cli_processor.cpp
index ae162793a..bb5d97ee7 100644
--- a/src/app/cli/cli_processor.cpp
+++ b/src/app/cli/cli_processor.cpp
@@ -29,7 +29,6 @@
 #include "doc/frame_tag.h"
 #include "doc/frame_tags.h"
 #include "doc/layer.h"
-#include "doc/layers_range.h"
 
 namespace app {
 
@@ -332,7 +331,7 @@ bool CliProcessor::openFile(CliOpenFile& cof)
   if (doc) {
     // Show all layers
     if (cof.allLayers) {
-      for (doc::Layer* layer : doc->sprite()->layers())
+      for (doc::Layer* layer : doc->sprite()->allLayers())
         layer->setVisible(true);
     }
 
@@ -360,7 +359,7 @@ bool CliProcessor::openFile(CliOpenFile& cof)
 
       if (!cof.importLayer.empty()) {
         Layer* foundLayer = nullptr;
-        for (Layer* layer : doc->sprite()->layers()) {
+        for (Layer* layer : doc->sprite()->allLayers()) {
           if (layer->name() == cof.importLayer) {
             foundLayer = layer;
             break;
@@ -370,10 +369,8 @@ bool CliProcessor::openFile(CliOpenFile& cof)
           m_exporter->addDocument(doc, foundLayer, frameTag, isTemporalTag);
       }
       else if (cof.splitLayers) {
-        for (auto layer : doc->sprite()->layers()) {
-          if (layer->isVisible())
-            m_exporter->addDocument(doc, layer, frameTag, isTemporalTag);
-        }
+        for (auto layer : doc->sprite()->allVisibleLayers())
+          m_exporter->addDocument(doc, layer, frameTag, isTemporalTag);
       }
       else {
         m_exporter->addDocument(doc, nullptr, frameTag, isTemporalTag);
@@ -407,9 +404,10 @@ void CliProcessor::saveFile(const CliOpenFile& cof)
   }
 
   // Store in "visibility" the original "visible" state of every layer.
-  std::vector<bool> visibility(doc->sprite()->countLayers());
+  LayerList allLayers = doc->sprite()->allLayers();
+  std::vector<bool> visibility(allLayers.size());
   int i = 0;
-  for (doc::Layer* layer : doc->sprite()->layers())
+  for (doc::Layer* layer : allLayers)
     visibility[i++] = layer->isVisible();
 
   std::string fn = cof.filename;
@@ -427,13 +425,13 @@ void CliProcessor::saveFile(const CliOpenFile& cof)
   std::vector<doc::Layer*> layers;
   // --save-as with --split-layers or --split-tags
   if (cof.splitLayers) {
-    for (doc::Layer* layer : doc->sprite()->layers())
+    for (doc::Layer* layer : doc->sprite()->allVisibleLayers())
       layers.push_back(layer);
   }
   else {
     // Show only one layer
     if (!cof.importLayer.empty()) {
-      for (Layer* layer : doc->sprite()->layers()) {
+      for (Layer* layer : allLayers) {
         if (layer->name() == cof.importLayer) {
           layer->setVisible(true);
           layers.push_back(layer);
@@ -481,7 +479,7 @@ void CliProcessor::saveFile(const CliOpenFile& cof)
           continue;     // Just ignore this layer.
 
         // Make this layer ("show") the only one visible.
-        for (doc::Layer* hide : doc->sprite()->layers())
+        for (doc::Layer* hide : allLayers)
           hide->setVisible(hide == layer);
       }
 
@@ -521,7 +519,7 @@ void CliProcessor::saveFile(const CliOpenFile& cof)
 
   // Restore layer visibility
   i = 0;
-  for (Layer* layer : doc->sprite()->layers())
+  for (Layer* layer : allLayers)
     layer->setVisible(visibility[i++]);
 
   // Undo crop
diff --git a/src/app/cli/default_cli_delegate.cpp b/src/app/cli/default_cli_delegate.cpp
index 533ddcf5c..1f8b3e292 100644
--- a/src/app/cli/default_cli_delegate.cpp
+++ b/src/app/cli/default_cli_delegate.cpp
@@ -22,7 +22,6 @@
 #include "base/convert_to.h"
 #include "doc/frame_tag.h"
 #include "doc/layer.h"
-#include "doc/layers_range.h"
 #include "doc/sprite.h"
 #include "script/engine_delegate.h"
 
@@ -53,10 +52,8 @@ void DefaultCliDelegate::afterOpenFile(const CliOpenFile& cof)
     return;
 
   if (cof.listLayers) {
-    for (doc::Layer* layer : cof.document->sprite()->layers()) {
-      if (layer->isVisible())
-        std::cout << layer->name() << "\n";
-    }
+    for (doc::Layer* layer : cof.document->sprite()->allVisibleLayers())
+      std::cout << layer->name() << "\n";
   }
 
   if (cof.listTags) {
diff --git a/src/app/cmd.cpp b/src/app/cmd.cpp
index f44727755..00eecc2a3 100644
--- a/src/app/cmd.cpp
+++ b/src/app/cmd.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -13,6 +13,9 @@
 
 #include <typeinfo>
 
+// Uncomment this in case you want to check what Cmd is being executed on each step
+//#define TRACE_CMD
+
 namespace app {
 
 Cmd::Cmd()
@@ -28,7 +31,9 @@ Cmd::~Cmd()
 
 void Cmd::execute(Context* ctx)
 {
+#if TRACE_CMD
   TRACE("Cmd: Executing cmd '%s'\n", typeid(*this).name());
+#endif
   ASSERT(m_state == State::NotExecuted);
 
   m_ctx = ctx;
@@ -43,7 +48,9 @@ void Cmd::execute(Context* ctx)
 
 void Cmd::undo()
 {
+#if TRACE_CMD
   TRACE("Cmd: Undo cmd '%s'\n", typeid(*this).name());
+#endif
   ASSERT(m_state == State::Executed || m_state == State::Redone);
 
   onUndo();
@@ -56,7 +63,9 @@ void Cmd::undo()
 
 void Cmd::redo()
 {
+#if TRACE_CMD
   TRACE("Cmd: Redo cmd '%s'\n", typeid(*this).name());
+#endif
   ASSERT(m_state == State::Undone);
 
   onRedo();
diff --git a/src/app/cmd/add_cel.cpp b/src/app/cmd/add_cel.cpp
index 0c7448a15..aad94f854 100644
--- a/src/app/cmd/add_cel.cpp
+++ b/src/app/cmd/add_cel.cpp
@@ -39,6 +39,8 @@ void AddCel::onExecute()
 {
   Layer* layer = this->layer();
   Cel* cel = this->cel();
+  ASSERT(layer);
+  ASSERT(cel);
 
   addCel(layer, cel);
 }
@@ -47,6 +49,8 @@ void AddCel::onUndo()
 {
   Layer* layer = this->layer();
   Cel* cel = this->cel();
+  ASSERT(layer);
+  ASSERT(cel);
 
   // Save the CelData only if the cel isn't linked
   bool has_data = (cel->links() == 0);
@@ -64,6 +68,7 @@ void AddCel::onUndo()
 void AddCel::onRedo()
 {
   Layer* layer = this->layer();
+  ASSERT(layer);
 
   SubObjectsFromSprite io(layer->sprite());
   bool has_data = (read8(m_stream) != 0);
@@ -75,6 +80,7 @@ void AddCel::onRedo()
     io.addCelDataRef(celdata);
   }
   Cel* cel = read_cel(m_stream, &io);
+  ASSERT(cel);
 
   addCel(layer, cel);
 
diff --git a/src/app/cmd/add_layer.cpp b/src/app/cmd/add_layer.cpp
index 3d9241ff7..80ed36087 100644
--- a/src/app/cmd/add_layer.cpp
+++ b/src/app/cmd/add_layer.cpp
@@ -22,8 +22,8 @@ namespace cmd {
 
 using namespace doc;
 
-AddLayer::AddLayer(Layer* folder, Layer* newLayer, Layer* afterThis)
-  : m_folder(folder)
+AddLayer::AddLayer(Layer* group, Layer* newLayer, Layer* afterThis)
+  : m_group(group)
   , m_newLayer(newLayer)
   , m_afterThis(afterThis)
   , m_size(0)
@@ -32,61 +32,62 @@ AddLayer::AddLayer(Layer* folder, Layer* newLayer, Layer* afterThis)
 
 void AddLayer::onExecute()
 {
-  Layer* folder = m_folder.layer();
+  Layer* group = m_group.layer();
   Layer* newLayer = m_newLayer.layer();
   Layer* afterThis = m_afterThis.layer();
 
-  addLayer(folder, newLayer, afterThis);
+  addLayer(group, newLayer, afterThis);
 }
 
 void AddLayer::onUndo()
 {
-  Layer* folder = m_folder.layer();
+  Layer* group = m_group.layer();
   Layer* layer = m_newLayer.layer();
 
   write_layer(m_stream, layer);
   m_size = size_t(m_stream.tellp());
 
-  removeLayer(folder, layer);
+  removeLayer(group, layer);
 }
 
 void AddLayer::onRedo()
 {
-  Layer* folder = m_folder.layer();
-  SubObjectsFromSprite io(folder->sprite());
+  Layer* group = m_group.layer();
+  SubObjectsFromSprite io(group->sprite());
   Layer* newLayer = read_layer(m_stream, &io);
   Layer* afterThis = m_afterThis.layer();
 
-  addLayer(folder, newLayer, afterThis);
+  addLayer(group, newLayer, afterThis);
 
   m_stream.str(std::string());
   m_stream.clear();
   m_size = 0;
 }
 
-void AddLayer::addLayer(Layer* folder, Layer* newLayer, Layer* afterThis)
+void AddLayer::addLayer(Layer* group, Layer* newLayer, Layer* afterThis)
 {
-  static_cast<LayerFolder*>(folder)->addLayer(newLayer);
-  static_cast<LayerFolder*>(folder)->stackLayer(newLayer, afterThis);
-  folder->incrementVersion();
+  static_cast<LayerGroup*>(group)->insertLayer(newLayer, afterThis);
+  group->incrementVersion();
+  group->sprite()->incrementVersion();
 
-  Document* doc = folder->sprite()->document();
+  Document* doc = group->sprite()->document();
   DocumentEvent ev(doc);
-  ev.sprite(folder->sprite());
+  ev.sprite(group->sprite());
   ev.layer(newLayer);
   doc->notifyObservers<DocumentEvent&>(&DocumentObserver::onAddLayer, ev);
 }
 
-void AddLayer::removeLayer(Layer* folder, Layer* layer)
+void AddLayer::removeLayer(Layer* group, Layer* layer)
 {
-  Document* doc = folder->sprite()->document();
+  Document* doc = group->sprite()->document();
   DocumentEvent ev(doc);
   ev.sprite(layer->sprite());
   ev.layer(layer);
   doc->notifyObservers<DocumentEvent&>(&DocumentObserver::onBeforeRemoveLayer, ev);
 
-  static_cast<LayerFolder*>(folder)->removeLayer(layer);
-  folder->incrementVersion();
+  static_cast<LayerGroup*>(group)->removeLayer(layer);
+  group->incrementVersion();
+  layer->sprite()->incrementVersion();
 
   doc->notifyObservers<DocumentEvent&>(&DocumentObserver::onAfterRemoveLayer, ev);
 
diff --git a/src/app/cmd/add_layer.h b/src/app/cmd/add_layer.h
index d9f52f18d..76844cbf2 100644
--- a/src/app/cmd/add_layer.h
+++ b/src/app/cmd/add_layer.h
@@ -24,7 +24,7 @@ namespace cmd {
 
   class AddLayer : public Cmd {
   public:
-    AddLayer(Layer* folder, Layer* newLayer, Layer* afterThis);
+    AddLayer(Layer* group, Layer* newLayer, Layer* afterThis);
 
   protected:
     void onExecute() override;
@@ -35,10 +35,10 @@ namespace cmd {
     }
 
   private:
-    void addLayer(Layer* folder, Layer* newLayer, Layer* afterThis);
-    void removeLayer(Layer* folder, Layer* layer);
+    void addLayer(Layer* group, Layer* newLayer, Layer* afterThis);
+    void removeLayer(Layer* group, Layer* layer);
 
-    WithLayer m_folder;
+    WithLayer m_group;
     WithLayer m_newLayer;
     WithLayer m_afterThis;
     size_t m_size;
diff --git a/src/app/cmd/configure_background.cpp b/src/app/cmd/configure_background.cpp
index 4f835d471..190fa1c06 100644
--- a/src/app/cmd/configure_background.cpp
+++ b/src/app/cmd/configure_background.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -15,6 +15,7 @@
 #include "app/cmd/set_layer_flags.h"
 #include "app/cmd/set_layer_name.h"
 #include "app/cmd/set_layer_opacity.h"
+#include "doc/sprite.h"
 
 namespace app {
 namespace cmd {
@@ -33,7 +34,7 @@ ConfigureBackground::ConfigureBackground(Layer* layer)
     add(new cmd::SetLayerOpacity(static_cast<LayerImage*>(layer), 255));
   }
 
-  add(new cmd::MoveLayer(layer, nullptr));
+  add(new cmd::MoveLayer(layer, layer->sprite()->root(), nullptr));
 }
 
 } // namespace cmd
diff --git a/src/app/cmd/copy_frame.cpp b/src/app/cmd/copy_frame.cpp
index 531063129..ba3f33465 100644
--- a/src/app/cmd/copy_frame.cpp
+++ b/src/app/cmd/copy_frame.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -41,8 +41,7 @@ void CopyFrame::onExecute()
   if (fromFrame >= m_newFrame)
     ++fromFrame;
 
-  for (int i=0; i<sprite->countLayers(); ++i) {
-    Layer* layer = sprite->layer(i);
+  for (Layer* layer : sprite->allLayers()) {
     if (layer->isImage())  {
       executeAndAdd(new cmd::CopyCel(
           static_cast<LayerImage*>(layer), fromFrame,
diff --git a/src/app/cmd/flatten_layers.cpp b/src/app/cmd/flatten_layers.cpp
index a588b68d7..a634598a0 100644
--- a/src/app/cmd/flatten_layers.cpp
+++ b/src/app/cmd/flatten_layers.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -56,7 +56,7 @@ void FlattenLayers::onExecute()
     // Create a new transparent layer to flatten everything onto.
     flatLayer = new LayerImage(sprite);
     ASSERT(flatLayer->isVisible());
-    executeAndAdd(new cmd::AddLayer(sprite->folder(), flatLayer, nullptr));
+    executeAndAdd(new cmd::AddLayer(sprite->root(), flatLayer, nullptr));
     executeAndAdd(new cmd::SetLayerName(flatLayer, "Flattened"));
     bgcolor = sprite->transparentColor();
   }
@@ -92,7 +92,7 @@ void FlattenLayers::onExecute()
   }
 
   // Delete old layers.
-  LayerList layers = sprite->folder()->getLayersList();
+  LayerList layers = sprite->root()->layers();
   for (Layer* layer : layers)
     if (layer != flatLayer)
       executeAndAdd(new cmd::RemoveLayer(layer));
diff --git a/src/app/cmd/move_layer.cpp b/src/app/cmd/move_layer.cpp
index e0f62fd32..e50fc87b1 100644
--- a/src/app/cmd/move_layer.cpp
+++ b/src/app/cmd/move_layer.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -21,29 +21,53 @@ namespace cmd {
 
 using namespace doc;
 
-MoveLayer::MoveLayer(Layer* layer, Layer* afterThis)
+MoveLayer::MoveLayer(Layer* layer,
+                     Layer* newParent,
+                     Layer* afterThis)
   : m_layer(layer)
+  , m_oldParent(layer->parent())
   , m_oldAfterThis(layer->getPrevious())
-  , m_newAfterThis(afterThis)
+  , m_newParent(newParent)
+  , m_newAfterThis(afterThis == layer ? afterThis->getPrevious(): afterThis)
 {
 }
 
 void MoveLayer::onExecute()
 {
-  m_layer.layer()->parent()->stackLayer(
-    m_layer.layer(),
-    m_newAfterThis.layer());
+  Layer* layer = m_layer.layer();
+  Layer* afterThis = m_newAfterThis.layer();
+  LayerGroup* oldParent = static_cast<LayerGroup*>(m_oldParent.layer());
+  LayerGroup* newParent = static_cast<LayerGroup*>(m_newParent.layer());
+  ASSERT(layer);
+  ASSERT(oldParent);
+  ASSERT(newParent);
 
-  m_layer.layer()->parent()->incrementVersion();
+  oldParent->removeLayer(layer);
+  newParent->insertLayer(layer, afterThis);
+
+  if (oldParent != newParent)
+    oldParent->incrementVersion();
+  newParent->incrementVersion();
+  layer->sprite()->incrementVersion();
 }
 
 void MoveLayer::onUndo()
 {
-  m_layer.layer()->parent()->stackLayer(
-    m_layer.layer(),
-    m_oldAfterThis.layer());
+  Layer* layer = m_layer.layer();
+  Layer* afterThis = m_oldAfterThis.layer();
+  LayerGroup* oldParent = static_cast<LayerGroup*>(m_oldParent.layer());
+  LayerGroup* newParent = static_cast<LayerGroup*>(m_newParent.layer());
+  ASSERT(layer);
+  ASSERT(oldParent);
+  ASSERT(newParent);
 
-  m_layer.layer()->parent()->incrementVersion();
+  newParent->removeLayer(layer);
+  oldParent->insertLayer(layer, afterThis);
+
+  if (oldParent != newParent)
+    oldParent->incrementVersion();
+  newParent->incrementVersion();
+  layer->sprite()->incrementVersion();
 }
 
 void MoveLayer::onFireNotifications()
diff --git a/src/app/cmd/move_layer.h b/src/app/cmd/move_layer.h
index 6f73fc903..716828ad6 100644
--- a/src/app/cmd/move_layer.h
+++ b/src/app/cmd/move_layer.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -18,7 +18,9 @@ namespace cmd {
 
   class MoveLayer : public Cmd {
   public:
-    MoveLayer(Layer* layer, Layer* afterThis);
+    MoveLayer(Layer* layer,
+              Layer* newParent,
+              Layer* afterThis);
 
   protected:
     void onExecute() override;
@@ -30,8 +32,8 @@ namespace cmd {
 
   private:
     WithLayer m_layer;
-    WithLayer m_oldAfterThis;
-    WithLayer m_newAfterThis;
+    WithLayer m_oldParent, m_oldAfterThis;
+    WithLayer m_newParent, m_newAfterThis;
   };
 
 } // namespace cmd
diff --git a/src/app/cmd_transaction.cpp b/src/app/cmd_transaction.cpp
index a3f92c4c6..aad3b7cc9 100644
--- a/src/app/cmd_transaction.cpp
+++ b/src/app/cmd_transaction.cpp
@@ -65,7 +65,7 @@ std::string CmdTransaction::onLabel() const
 doc::SpritePosition CmdTransaction::calcSpritePosition()
 {
   doc::Site site = context()->activeSite();
-  return doc::SpritePosition(site.layerIndex(), site.frame());
+  return doc::SpritePosition(site.layer(), site.frame());
 }
 
 } // namespace app
diff --git a/src/app/commands/cmd_cel_properties.cpp b/src/app/commands/cmd_cel_properties.cpp
index 533228810..42dbe5752 100644
--- a/src/app/commands/cmd_cel_properties.cpp
+++ b/src/app/commands/cmd_cel_properties.cpp
@@ -108,9 +108,8 @@ private:
     else if (m_range.enabled()) {
       Sprite* sprite = m_document->sprite();
       int count = 0;
-      for (Cel* cel : sprite->uniqueCels(m_range.frameBegin(),
-                                         m_range.frameEnd())) {
-        if (m_range.inRange(sprite->layerToIndex(cel->layer()))) {
+      for (Cel* cel : sprite->uniqueCels(m_range.selectedFrames())) {
+        if (m_range.contains(cel->layer())) {
           if (backgroundCount && cel->layer()->isBackground())
             ++(*backgroundCount);
           ++count;
@@ -170,37 +169,28 @@ private:
         ContextWriter writer(UIContext::instance());
         Transaction transaction(writer.context(), "Set Cel Properties");
 
-        if (count == 1 && m_cel) {
-          if (!m_cel->layer()->isBackground() &&
-              newOpacity != m_cel->opacity()) {
-            transaction.execute(new cmd::SetCelOpacity(writer.cel(), newOpacity));
-          }
-
-          if (m_userData != m_cel->data()->userData()) {
-            transaction.execute(new cmd::SetUserData(writer.cel()->data(), m_userData));
-
-            // Redraw timeline because the cel's user data/color
-            // might have changed.
-            App::instance()->timeline()->invalidate();
-          }
+        DocumentRange range;
+        if (m_range.enabled())
+          range = m_range;
+        else {
+          range.startRange(m_cel->layer(), m_cel->frame(), DocumentRange::kCels);
+          range.endRange(m_cel->layer(), m_cel->frame());
         }
-        else if (m_range.enabled()) {
-          Sprite* sprite = m_document->sprite();
-          for (Cel* cel : sprite->uniqueCels(m_range.frameBegin(),
-                                             m_range.frameEnd())) {
-            if (m_range.inRange(sprite->layerToIndex(cel->layer()))) {
-              if (!cel->layer()->isBackground() && newOpacity != cel->opacity()) {
-                transaction.execute(new cmd::SetCelOpacity(cel, newOpacity));
-              }
 
-              if (m_newUserData &&
-                  m_userData != cel->data()->userData()) {
-                transaction.execute(new cmd::SetUserData(cel->data(), m_userData));
+        Sprite* sprite = m_document->sprite();
+        for (Cel* cel : sprite->uniqueCels(range.selectedFrames())) {
+          if (range.contains(cel->layer())) {
+            if (!cel->layer()->isBackground() && newOpacity != cel->opacity()) {
+              transaction.execute(new cmd::SetCelOpacity(cel, newOpacity));
+            }
 
-                // Redraw timeline because the cel's user data/color
-                // might have changed.
-                App::instance()->timeline()->invalidate();
-              }
+            if (m_newUserData &&
+                m_userData != cel->data()->userData()) {
+              transaction.execute(new cmd::SetUserData(cel->data(), m_userData));
+
+              // Redraw timeline because the cel's user data/color
+              // might have changed.
+              App::instance()->timeline()->invalidate();
             }
           }
         }
diff --git a/src/app/commands/cmd_clear_cel.cpp b/src/app/commands/cmd_clear_cel.cpp
index c20d835cc..f58e532cb 100644
--- a/src/app/commands/cmd_clear_cel.cpp
+++ b/src/app/commands/cmd_clear_cel.cpp
@@ -16,7 +16,6 @@
 #include "app/modules/gui.h"
 #include "app/transaction.h"
 #include "app/ui/status_bar.h"
-#include "app/ui/timeline.h"
 #include "doc/cel.h"
 #include "doc/layer.h"
 #include "doc/sprite.h"
@@ -53,33 +52,29 @@ void ClearCelCommand::onExecute(Context* context)
   {
     Transaction transaction(writer.context(), "Clear Cel");
 
-    // TODO the range of selected frames should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    if (range.enabled()) {
-      Sprite* sprite = writer.sprite();
-
-      for (LayerIndex layerIdx = range.layerBegin(); layerIdx <= range.layerEnd(); ++layerIdx) {
-        Layer* layer = sprite->indexToLayer(layerIdx);
+    const Site* site = writer.site();
+    if (site->inTimeline() &&
+        !site->selectedLayers().empty() &&
+        !site->selectedFrames().empty()) {
+      for (Layer* layer : site->selectedLayers()) {
         if (!layer->isImage())
           continue;
 
+        if (!layer->isEditableHierarchy()) {
+          nonEditableLayers = true;
+          continue;
+        }
+
         LayerImage* layerImage = static_cast<LayerImage*>(layer);
 
-        for (frame_t frame = range.frameEnd(),
-               begin = range.frameBegin()-1;
-             frame != begin;
-             --frame) {
-          if (layerImage->cel(frame)) {
-            if (layerImage->isEditable())
-              document->getApi(transaction).clearCel(layerImage, frame);
-            else
-              nonEditableLayers = true;
-          }
+        for (frame_t frame : site->selectedFrames().reversed()) {
+          if (layerImage->cel(frame))
+            document->getApi(transaction).clearCel(layerImage, frame);
         }
       }
     }
     else if (writer.cel()) {
-      if (writer.layer()->isEditable())
+      if (writer.layer()->isEditableHierarchy())
         document->getApi(transaction).clearCel(writer.cel());
       else
         nonEditableLayers = true;
diff --git a/src/app/commands/cmd_duplicate_layer.cpp b/src/app/commands/cmd_duplicate_layer.cpp
index a2cf34193..7f73569b3 100644
--- a/src/app/commands/cmd_duplicate_layer.cpp
+++ b/src/app/commands/cmd_duplicate_layer.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -58,7 +58,9 @@ void DuplicateLayerCommand::onExecute(Context* context)
     Transaction transaction(writer.context(), "Layer Duplication");
     LayerImage* sourceLayer = static_cast<LayerImage*>(writer.layer());
     DocumentApi api = document->getApi(transaction);
-    api.duplicateLayerAfter(sourceLayer, sourceLayer);
+    api.duplicateLayerAfter(sourceLayer,
+                            sourceLayer->parent(),
+                            sourceLayer);
     transaction.commit();
   }
 
diff --git a/src/app/commands/cmd_export_sprite_sheet.cpp b/src/app/commands/cmd_export_sprite_sheet.cpp
index 78c7a01a6..4178fd2b7 100644
--- a/src/app/commands/cmd_export_sprite_sheet.cpp
+++ b/src/app/commands/cmd_export_sprite_sheet.cpp
@@ -164,7 +164,7 @@ namespace {
       // TODO the range of selected frames should be in doc::Site.
       auto range = App::instance()->timeline()->range();
       if (range.enabled()) {
-        return range.frameBegin();
+        return range.firstFrame();
       }
       else if (current_editor) {
         return current_editor->frame();
@@ -176,7 +176,7 @@ namespace {
     static frame_t To() {
       auto range = App::instance()->timeline()->range();
       if (range.enabled()) {
-        return range.frameEnd();
+        return range.lastFrame();
       }
       else if (current_editor) {
         return current_editor->frame();
@@ -218,20 +218,20 @@ namespace {
       if (!range.enabled()) {
         if (current_editor) {
           ASSERT(current_editor->sprite() == sprite);
-          range.startRange(sprite->layerToIndex(current_editor->layer()),
+          range.clearRange();
+          range.startRange(current_editor->layer(),
                            current_editor->frame(), DocumentRange::kCels);
-          range.endRange(sprite->layerToIndex(current_editor->layer()),
+          range.endRange(current_editor->layer(),
                          current_editor->frame());
         }
         else
           return;
       }
 
-      std::vector<Layer*> layers;
-      sprite->getLayersList(layers);
+      LayerList layers = sprite->allLayers();
       for (int i=0; i<int(layers.size()); ++i) {
         Layer* layer = layers[i];
-        bool selected = range.inRange(LayerIndex(i));
+        bool selected = range.contains(layer);
 
         if (selected != layer->isVisible()) {
           m_restore.push_back(std::make_pair(layer, layer->isVisible()));
@@ -251,11 +251,23 @@ public:
   class LayerItem : public ListItem {
   public:
     LayerItem(Layer* layer)
-      : ListItem("Layer: " + layer->name())
+      : ListItem(buildName(layer))
       , m_layer(layer) {
     }
     Layer* layer() const { return m_layer; }
   private:
+    static std::string buildName(const Layer* layer) {
+      bool isGroup = layer->isGroup();
+      std::string name;
+      while (layer != layer->sprite()->root()) {
+        if (!name.empty())
+          name.insert(0, " > ");
+        name.insert(0, layer->name());
+        layer = layer->parent();
+      }
+      name.insert(0, isGroup ? "Group: ": "Layer: ");
+      return name;
+    }
     Layer* m_layer;
   };
 
@@ -297,9 +309,9 @@ public:
     if (m_docPref.spriteSheet.layer() == kSelectedLayers)
       layers()->setSelectedItemIndex(i);
     {
-      std::vector<Layer*> layersList;
-      m_sprite->getLayersList(layersList);
-      for (Layer* layer : layersList) {
+      LayerList layersList = m_sprite->allLayers();
+      for (auto it=layersList.rbegin(), end=layersList.rend(); it!=end; ++it) {
+        Layer* layer = *it;
         i = layers()->addItem(new LayerItem(layer));
         if (m_docPref.spriteSheet.layer() == layer->name())
           layers()->setSelectedItemIndex(i);
@@ -837,8 +849,7 @@ void ExportSpriteSheetCommand::onExecute(Context* context)
   }
   else {
     // TODO add a getLayerByName
-    std::vector<Layer*> layers;
-    sprite->getLayersList(layers);
+    LayerList layers = sprite->allLayers();
     for (Layer* l : layers) {
       if (l->name() == layerName) {
         layer = l;
diff --git a/src/app/commands/cmd_frame_properties.cpp b/src/app/commands/cmd_frame_properties.cpp
index dd52bbcb9..99261d3bc 100644
--- a/src/app/commands/cmd_frame_properties.cpp
+++ b/src/app/commands/cmd_frame_properties.cpp
@@ -10,11 +10,11 @@
 #endif
 
 #include "app/app.h"
+#include "app/context.h"
 #include "app/commands/command.h"
 #include "app/commands/params.h"
 #include "app/context_access.h"
 #include "app/document_api.h"
-#include "app/ui/timeline.h"
 #include "app/transaction.h"
 #include "base/convert_to.h"
 #include "doc/sprite.h"
@@ -82,51 +82,58 @@ void FramePropertiesCommand::onExecute(Context* context)
   const Sprite* sprite = reader.sprite();
 
   app::gen::FrameProperties window;
-  frame_t firstFrame = 0;
-  frame_t lastFrame = 0;
+  SelectedFrames selFrames;
 
   switch (m_target) {
 
     case ALL_FRAMES:
-      lastFrame = sprite->lastFrame();
+      selFrames.insert(0, sprite->lastFrame());
       break;
 
     case CURRENT_RANGE: {
-      // TODO the range of selected frames should be in doc::Site.
-      auto range = App::instance()->timeline()->range();
-      if (range.enabled()) {
-        firstFrame = range.frameBegin();
-        lastFrame = range.frameEnd();
+      Site site = context->activeSite();
+      if (site.inTimeline()) {
+        selFrames = site.selectedFrames();
       }
       else {
-        firstFrame = lastFrame = reader.frame();
+        selFrames.insert(site.frame());
       }
       break;
     }
 
     case SPECIFIC_FRAME:
-      firstFrame = lastFrame = m_frame;
+      selFrames.insert(m_frame);
       break;
   }
 
-  if (firstFrame != lastFrame)
-    window.frame()->setTextf("[%d...%d]", (int)firstFrame+1, (int)lastFrame+1);
-  else
-    window.frame()->setTextf("%d", (int)firstFrame+1);
+  ASSERT(!selFrames.empty());
+  if (selFrames.empty())
+    return;
 
-  window.frlen()->setTextf("%d", sprite->frameDuration(firstFrame));
+  if (selFrames.size() == 1)
+    window.frame()->setTextf("%d", selFrames.firstFrame()+1);
+  else if (selFrames.ranges() == 1) {
+    window.frame()->setTextf("[%d...%d]",
+                             selFrames.firstFrame()+1,
+                             selFrames.lastFrame()+1);
+  }
+  else
+    window.frame()->setTextf("Multiple Frames");
+
+  window.frlen()->setTextf(
+    "%d", sprite->frameDuration(selFrames.firstFrame()));
 
   window.openWindowInForeground();
   if (window.closer() == window.ok()) {
-    int num = window.frlen()->textInt();
+    int newMsecs = window.frlen()->textInt();
 
     ContextWriter writer(reader);
     Transaction transaction(writer.context(), "Frame Duration");
     DocumentApi api = writer.document()->getApi(transaction);
-    if (firstFrame != lastFrame)
-      api.setFrameRangeDuration(writer.sprite(), firstFrame, lastFrame, num);
-    else
-      api.setFrameDuration(writer.sprite(), firstFrame, num);
+
+    for (frame_t frame : selFrames)
+      api.setFrameDuration(writer.sprite(), frame, newMsecs);
+
     transaction.commit();
   }
 }
diff --git a/src/app/commands/cmd_goto_layer.cpp b/src/app/commands/cmd_goto_layer.cpp
index bd27f7725..2ec052698 100644
--- a/src/app/commands/cmd_goto_layer.cpp
+++ b/src/app/commands/cmd_goto_layer.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -16,104 +16,98 @@
 #include "app/modules/gui.h"
 #include "app/ui/editor/editor.h"
 #include "app/ui/status_bar.h"
+#include "app/ui/timeline.h"
 #include "doc/layer.h"
 #include "doc/sprite.h"
 
 namespace app {
 
-class GotoCommand : public Command {
+class GotoLayerCommand : public Command {
 public:
-  GotoCommand(const char* short_name, const char* friendly_name, CommandFlags flags)
-    : Command(short_name, friendly_name, flags) {
+  GotoLayerCommand(int offset,
+                   const char* shortName,
+                   const char* friendlyName,
+                   CommandFlags flags)
+    : Command(shortName, friendlyName, flags),
+      m_offset(offset) {
   }
 
 protected:
+
+  bool onEnabled(Context* context) override {
+    return (current_editor &&
+            current_editor->document());
+  }
+
+  void onExecute(Context* context) override {
+    Site site = current_editor->getSite();
+
+    Layer* layer = site.layer();
+    if (!layer)
+      return;
+
+    if (m_offset > 0) {
+      int i = m_offset;
+      while (i-- > 0) {
+        layer = layer->getNextInWholeHierarchy();
+        if (!layer)
+          layer = site.sprite()->firstBrowsableLayer();
+      }
+    }
+    else if (m_offset < 0) {
+      int i = m_offset;
+      while (i++ < 0) {
+        layer = layer->getPreviousInWholeHierarchy();
+        if (!layer)
+          layer = site.sprite()->root()->lastLayer();
+      }
+    }
+
+    site.layer(layer);
+
+    // Flash the current layer
+    current_editor->setLayer(site.layer());
+    current_editor->flashCurrentLayer();
+
+    updateStatusBar(site);
+  }
+
   void updateStatusBar(Site& site) {
     if (site.layer() != NULL)
-      StatusBar::instance()
-        ->setStatusText(1000, "Layer `%s' selected",
-          site.layer()->name().c_str());
+      StatusBar::instance()->setStatusText(
+        1000, "%s '%s' selected",
+        (site.layer()->isGroup() ? "Group": "Layer"),
+        site.layer()->name().c_str());
+  }
+
+private:
+  int m_offset;
+};
+
+class GotoPreviousLayerCommand : public GotoLayerCommand {
+public:
+  GotoPreviousLayerCommand()
+    : GotoLayerCommand(-1, "GotoPreviousLayer",
+                       "Go to Previous Layer",
+                       CmdUIOnlyFlag) {
+  }
+  Command* clone() const override {
+    return new GotoPreviousLayerCommand(*this);
   }
 };
 
-class GotoPreviousLayerCommand : public GotoCommand {
+class GotoNextLayerCommand : public GotoLayerCommand {
 public:
-  GotoPreviousLayerCommand();
-  Command* clone() const override { return new GotoPreviousLayerCommand(*this); }
-
-protected:
-  bool onEnabled(Context* context) override;
-  void onExecute(Context* context) override;
+  GotoNextLayerCommand()
+    : GotoLayerCommand(+1, "GotoNextLayer",
+                       "Go to Next Layer",
+                       CmdUIOnlyFlag) {
+  }
+  Command* clone() const override {
+    return new GotoNextLayerCommand(*this);
+  }
 };
 
-GotoPreviousLayerCommand::GotoPreviousLayerCommand()
- : GotoCommand("GotoPreviousLayer",
-               "Go to Previous Layer",
-               CmdUIOnlyFlag)
-{
-}
-
-bool GotoPreviousLayerCommand::onEnabled(Context* context)
-{
-  return (current_editor != nullptr &&
-          current_editor->document());
-}
-
-void GotoPreviousLayerCommand::onExecute(Context* context)
-{
-  Site site = current_editor->getSite();
-
-  if (site.layerIndex() > 0)
-    site.layerIndex(site.layerIndex().previous());
-  else
-    site.layerIndex(LayerIndex(site.sprite()->countLayers()-1));
-
-  // Flash the current layer
-  current_editor->setLayer(site.layer());
-  current_editor->flashCurrentLayer();
-
-  updateStatusBar(site);
-}
-
-class GotoNextLayerCommand : public GotoCommand {
-public:
-  GotoNextLayerCommand();
-  Command* clone() const override { return new GotoNextLayerCommand(*this); }
-
-protected:
-  bool onEnabled(Context* context) override;
-  void onExecute(Context* context) override;
-};
-
-GotoNextLayerCommand::GotoNextLayerCommand()
-  : GotoCommand("GotoNextLayer",
-                "Go to Next Layer",
-                CmdUIOnlyFlag)
-{
-}
-
-bool GotoNextLayerCommand::onEnabled(Context* context)
-{
-  return (current_editor != nullptr &&
-          current_editor->document());
-}
-
-void GotoNextLayerCommand::onExecute(Context* context)
-{
-  Site site = current_editor->getSite();
-
-  if (site.layerIndex() < site.sprite()->countLayers()-1)
-    site.layerIndex(site.layerIndex().next());
-  else
-    site.layerIndex(LayerIndex(0));
-
-  // Flash the current layer
-  current_editor->setLayer(site.layer());
-  current_editor->flashCurrentLayer();
-
-  updateStatusBar(site);
-}
-
 Command* CommandFactory::createGotoPreviousLayerCommand()
 {
   return new GotoPreviousLayerCommand;
diff --git a/src/app/commands/cmd_import_sprite_sheet.cpp b/src/app/commands/cmd_import_sprite_sheet.cpp
index e0598e12a..ac50068c5 100644
--- a/src/app/commands/cmd_import_sprite_sheet.cpp
+++ b/src/app/commands/cmd_import_sprite_sheet.cpp
@@ -394,7 +394,7 @@ void ImportSpriteSheetCommand::onExecute(Context* context)
     DocumentApi api = document->getApi(transaction);
 
     // Add the layer in the sprite.
-    LayerImage* resultLayer = api.newLayer(sprite, "Sprite Sheet");
+    LayerImage* resultLayer = api.newLayer(sprite->root(), "Sprite Sheet");
 
     // Add all frames+cels to the new layer
     for (size_t i=0; i<animation.size(); ++i) {
@@ -407,12 +407,12 @@ void ImportSpriteSheetCommand::onExecute(Context* context)
     }
 
     // Copy the list of layers (because we will modify it in the iteration).
-    LayerList layers = sprite->folder()->getLayersList();
+    LayerList layers = sprite->root()->layers();
 
     // Remove all other layers
-    for (LayerIterator it=layers.begin(), end=layers.end(); it!=end; ++it) {
-      if (*it != resultLayer)
-        api.removeLayer(*it);
+    for (Layer* child : layers) {
+      if (child != resultLayer)
+        api.removeLayer(child);
     }
 
     // Change the number of frames
diff --git a/src/app/commands/cmd_layer_properties.cpp b/src/app/commands/cmd_layer_properties.cpp
index 34817356d..0b512b918 100644
--- a/src/app/commands/cmd_layer_properties.cpp
+++ b/src/app/commands/cmd_layer_properties.cpp
@@ -96,14 +96,14 @@ public:
     UIContext::instance()->removeObserver(this);
   }
 
-  void setLayer(LayerImage* layer) {
+  void setLayer(Layer* layer) {
     if (m_layer) {
       document()->removeObserver(this);
       m_layer = nullptr;
     }
 
     m_timer.stop();
-    m_layer = const_cast<LayerImage*>(layer);
+    m_layer = layer;
 
     if (m_layer)
       document()->addObserver(this);
@@ -178,9 +178,10 @@ private:
     BlendMode newBlendMode = blendModeValue();
 
     if (newName != m_layer->name() ||
-        newOpacity != m_layer->opacity() ||
-        newBlendMode != m_layer->blendMode() ||
-        m_userData != m_layer->userData()) {
+        m_userData != m_layer->userData() ||
+        (m_layer->isImage() &&
+         (newOpacity != static_cast<LayerImage*>(m_layer)->opacity() ||
+          newBlendMode != static_cast<LayerImage*>(m_layer)->blendMode()))) {
       try {
         ContextWriter writer(UIContext::instance());
         Transaction transaction(writer.context(), "Set Layer Properties");
@@ -188,20 +189,21 @@ private:
         if (newName != m_layer->name())
           transaction.execute(new cmd::SetLayerName(writer.layer(), newName));
 
-        if (newOpacity != m_layer->opacity())
-          transaction.execute(new cmd::SetLayerOpacity(static_cast<LayerImage*>(writer.layer()), newOpacity));
-
-        if (newBlendMode != m_layer->blendMode())
-          transaction.execute(new cmd::SetLayerBlendMode(static_cast<LayerImage*>(writer.layer()), newBlendMode));
-
-        if (m_userData != m_layer->userData()) {
+        if (m_userData != m_layer->userData())
           transaction.execute(new cmd::SetUserData(writer.layer(), m_userData));
 
-          // Redraw timeline because the layer's user data/color
-          // might have changed.
-          App::instance()->timeline()->invalidate();
+        if (m_layer->isImage()) {
+          if (newOpacity != static_cast<LayerImage*>(m_layer)->opacity())
+            transaction.execute(new cmd::SetLayerOpacity(static_cast<LayerImage*>(writer.layer()), newOpacity));
+
+          if (newBlendMode != static_cast<LayerImage*>(m_layer)->blendMode())
+            transaction.execute(new cmd::SetLayerBlendMode(static_cast<LayerImage*>(writer.layer()), newBlendMode));
         }
 
+        // Redraw timeline because the layer's name/user data/color
+        // might have changed.
+        App::instance()->timeline()->invalidate();
+
         transaction.commit();
       }
       catch (const std::exception& e) {
@@ -215,7 +217,7 @@ private:
   // ContextObserver impl
   void onActiveSiteChange(const Site& site) override {
     if (isVisible())
-      setLayer(dynamic_cast<LayerImage*>(const_cast<Layer*>(site.layer())));
+      setLayer(const_cast<Layer*>(site.layer()));
     else if (m_layer)
       setLayer(nullptr);
   }
@@ -256,10 +258,18 @@ private:
     if (m_layer) {
       name()->setText(m_layer->name().c_str());
       name()->setEnabled(true);
-      mode()->setSelectedItemIndex((int)m_layer->blendMode());
-      mode()->setEnabled(!m_layer->isBackground());
-      opacity()->setValue(m_layer->opacity());
-      opacity()->setEnabled(!m_layer->isBackground());
+
+      if (m_layer->isImage()) {
+        mode()->setSelectedItemIndex((int)static_cast<LayerImage*>(m_layer)->blendMode());
+        mode()->setEnabled(!m_layer->isBackground());
+        opacity()->setValue(static_cast<LayerImage*>(m_layer)->opacity());
+        opacity()->setEnabled(!m_layer->isBackground());
+      }
+      else {
+        mode()->setEnabled(false);
+        opacity()->setEnabled(false);
+      }
+
       m_userData = m_layer->userData();
     }
     else {
@@ -272,7 +282,7 @@ private:
   }
 
   Timer m_timer;
-  LayerImage* m_layer;
+  Layer* m_layer;
   bool m_selfUpdate;
   UserData m_userData;
 };
diff --git a/src/app/commands/cmd_link_cels.cpp b/src/app/commands/cmd_link_cels.cpp
index db882636f..ebf2709a1 100644
--- a/src/app/commands/cmd_link_cels.cpp
+++ b/src/app/commands/cmd_link_cels.cpp
@@ -16,7 +16,6 @@
 #include "app/modules/gui.h"
 #include "app/transaction.h"
 #include "app/ui/status_bar.h"
-#include "app/ui/timeline.h"
 #include "doc/cel.h"
 #include "doc/layer.h"
 #include "doc/sprite.h"
@@ -43,9 +42,9 @@ LinkCelsCommand::LinkCelsCommand()
 bool LinkCelsCommand::onEnabled(Context* context)
 {
   if (context->checkFlags(ContextFlags::ActiveDocumentIsWritable)) {
-    // TODO the range of selected frames should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    return (range.enabled() && range.frames() > 1);
+    auto site = context->activeSite();
+    return (site.inTimeline() &&
+            site.selectedFrames().size() > 1);
   }
   else
     return false;
@@ -57,36 +56,33 @@ void LinkCelsCommand::onExecute(Context* context)
   Document* document(writer.document());
   bool nonEditableLayers = false;
   {
-    // TODO the range of selected frames should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    if (!range.enabled())
+    auto site = context->activeSite();
+    if (!site.inTimeline())
       return;
 
     Transaction transaction(writer.context(), friendlyName());
-    Sprite* sprite = writer.sprite();
-    frame_t begin = range.frameBegin();
-    frame_t end = range.frameEnd();
 
-    for (LayerIndex layerIdx = range.layerBegin(); layerIdx <= range.layerEnd(); ++layerIdx) {
-      Layer* layer = sprite->indexToLayer(layerIdx);
+    for (Layer* layer : site.selectedLayers()) {
       if (!layer->isImage())
         continue;
 
-      if (!layer->isEditable()) {
+      if (!layer->isEditableHierarchy()) {
         nonEditableLayers = true;
         continue;
       }
 
       LayerImage* layerImage = static_cast<LayerImage*>(layer);
-      for (frame_t frame=begin; frame < end+1; ++frame) {
+
+      for (auto it=site.selectedFrames().begin(), end=site.selectedFrames().end();
+           it != end; ++it) {
+        frame_t frame = *it;
         Cel* cel = layerImage->cel(frame);
         if (cel) {
-          for (frame = cel->frame()+1;
-               frame < end+1; ++frame) {
+          for (++it; it != end; ++it) {
             transaction.execute(
               new cmd::CopyCel(
                 layerImage, cel->frame(),
-                layerImage, frame,
+                layerImage, *it,
                 true));         // true = force links
           }
           break;
diff --git a/src/app/commands/cmd_new_file.cpp b/src/app/commands/cmd_new_file.cpp
index 10ea44fa0..9de977695 100644
--- a/src/app/commands/cmd_new_file.cpp
+++ b/src/app/commands/cmd_new_file.cpp
@@ -178,7 +178,7 @@ void NewFileCommand::onExecute(Context* context)
       // If the background color isn't transparent, we have to
       // convert the `Layer 1' in a `Background'
       if (color.getType() != app::Color::MaskType) {
-        Layer* layer = sprite->folder()->getFirstLayer();
+        Layer* layer = sprite->root()->firstLayer();
 
         if (layer && layer->isImage()) {
           LayerImage* layerImage = static_cast<LayerImage*>(layer);
diff --git a/src/app/commands/cmd_new_frame.cpp b/src/app/commands/cmd_new_frame.cpp
index 99fb04fbd..70c277856 100644
--- a/src/app/commands/cmd_new_frame.cpp
+++ b/src/app/commands/cmd_new_frame.cpp
@@ -106,34 +106,37 @@ void NewFrameCommand::onExecute(Context* context)
 
       case Content::DUPLICATE_CELS:
       case Content::DUPLICATE_CELS_BLOCK: {
-        // TODO the range of selected frames should be in doc::Site.
-        Timeline* timeline = App::instance()->timeline();
-        Timeline::Range range = timeline->range();
-        if (range.enabled()) {
+        const Site* site = writer.site();
+        if (site->inTimeline() &&
+            !site->selectedLayers().empty() &&
+            !site->selectedFrames().empty()) {
           std::map<CelData*, Cel*> relatedCels;
+
+          auto timeline = App::instance()->timeline();
           timeline->prepareToMoveRange();
+          DocumentRange range = timeline->range();
 
-          LayerIndex layerBegin = range.layerBegin();
-          LayerIndex layerEnd = range.layerEnd();
+          SelectedLayers selLayers;
+          if (site->inFrames())
+            selLayers.selectAllLayers(writer.sprite()->root());
+          else
+            selLayers = site->selectedLayers();
 
-          if (range.type() == DocumentRange::kFrames) {
-            layerBegin = writer.sprite()->firstLayer();
-            layerEnd = writer.sprite()->lastLayer();
-          }
+          frame_t frameRange =
+            (site->selectedFrames().lastFrame() -
+             site->selectedFrames().firstFrame() + 1);
 
-          for (LayerIndex layer = layerBegin; layer <= layerEnd; ++layer) {
-            Layer* layerPtr = writer.sprite()->indexToLayer(layer);
-            if (layerPtr->isImage()) {
-              for (frame_t frame = range.frameEnd(); frame >= range.frameBegin(); --frame) {
-                frame_t srcFrame = frame;
-                frame_t dstFrame = frame+range.frames();
+          for (Layer* layer : selLayers) {
+            if (layer->isImage()) {
+              for (frame_t srcFrame : site->selectedFrames().reversed()) {
+                frame_t dstFrame = srcFrame+frameRange;
                 bool continuous;
                 CelData* srcCelData = nullptr;
 
                 if (m_content == Content::DUPLICATE_CELS_BLOCK) {
                   continuous = false;
 
-                  Cel* srcCel = static_cast<LayerImage*>(layerPtr)->cel(srcFrame);
+                  Cel* srcCel = static_cast<LayerImage*>(layer)->cel(srcFrame);
                   if (srcCel) {
                     srcCelData = srcCel->data();
 
@@ -145,19 +148,19 @@ void NewFrameCommand::onExecute(Context* context)
                   }
                 }
                 else
-                  continuous = layerPtr->isContinuous();
+                  continuous = layer->isContinuous();
 
                 api.copyCel(
-                  static_cast<LayerImage*>(layerPtr), srcFrame,
-                  static_cast<LayerImage*>(layerPtr), dstFrame, continuous);
+                  static_cast<LayerImage*>(layer), srcFrame,
+                  static_cast<LayerImage*>(layer), dstFrame, continuous);
 
                 if (srcCelData && !relatedCels[srcCelData])
-                  relatedCels[srcCelData] = layerPtr->cel(dstFrame);
+                  relatedCels[srcCelData] = layer->cel(dstFrame);
               }
             }
           }
 
-          range.displace(0, range.frames());
+          range.displace(0, frameRange);
           timeline->moveRange(range);
         }
         else {
diff --git a/src/app/commands/cmd_new_frame_tag.cpp b/src/app/commands/cmd_new_frame_tag.cpp
index a7b5af3ee..386be462d 100644
--- a/src/app/commands/cmd_new_frame_tag.cpp
+++ b/src/app/commands/cmd_new_frame_tag.cpp
@@ -59,8 +59,8 @@ void NewFrameTagCommand::onExecute(Context* context)
   if (range.enabled() &&
       (range.type() == DocumentRange::kFrames ||
        range.type() == DocumentRange::kCels)) {
-    from = range.frameBegin();
-    to = range.frameEnd();
+    from = range.selectedFrames().firstFrame();
+    to = range.selectedFrames().lastFrame();
   }
 
   base::UniquePtr<FrameTag> frameTag(new FrameTag(from, to));
diff --git a/src/app/commands/cmd_new_layer.cpp b/src/app/commands/cmd_new_layer.cpp
index 3350efbde..dcbf139fc 100644
--- a/src/app/commands/cmd_new_layer.cpp
+++ b/src/app/commands/cmd_new_layer.cpp
@@ -10,6 +10,7 @@
 #endif
 
 #include "app/app.h"
+#include "app/cmd/move_layer.h"
 #include "app/commands/command.h"
 #include "app/commands/params.h"
 #include "app/context_access.h"
@@ -24,6 +25,8 @@
 #include "doc/sprite.h"
 #include "ui/ui.h"
 
+#include "new_layer.xml.h"
+
 #include <cstdio>
 #include <cstring>
 
@@ -42,14 +45,16 @@ protected:
   void onExecute(Context* context) override;
 
 private:
+  std::string getUniqueLayerName(const Sprite* sprite) const;
+  int getMaxLayerNum(const Layer* layer) const;
+  const char* layerPrefix() const;
+
   bool m_ask;
   bool m_top;
+  bool m_group;
   std::string m_name;
 };
 
-static std::string get_unique_layer_name(Sprite* sprite);
-static int get_max_layer_num(Layer* layer);
-
 NewLayerCommand::NewLayerCommand()
   : Command("NewLayer",
             "New Layer",
@@ -57,6 +62,7 @@ NewLayerCommand::NewLayerCommand()
 {
   m_ask = false;
   m_top = false;
+  m_group = false;
   m_name = "";
 }
 
@@ -64,6 +70,7 @@ void NewLayerCommand::onLoadParams(const Params& params)
 {
   m_ask = (params.get("ask") == "true");
   m_top = (params.get("top") == "true");
+  m_group = (params.get("group") == "true");
   m_name = params.get("name");
 }
 
@@ -84,66 +91,113 @@ void NewLayerCommand::onExecute(Context* context)
   if (!m_name.empty())
     name = m_name;
   else
-    name = get_unique_layer_name(sprite);
+    name = getUniqueLayerName(sprite);
 
   // If params specify to ask the user about the name...
   if (m_ask) {
     // We open the window to ask the name
-    base::UniquePtr<Window> window(app::load_widget<Window>("new_layer.xml", "new_layer"));
-    Widget* name_widget = app::find_widget<Widget>(window, "name");
-    name_widget->setText(name.c_str());
-    name_widget->setMinSize(gfx::Size(128, 0));
-
-    window->openWindowInForeground();
-
-    if (window->closer() != window->findChild("ok"))
+    app::gen::NewLayer window;
+    window.name()->setText(name.c_str());
+    window.name()->setMinSize(gfx::Size(128, 0));
+    window.openWindowInForeground();
+    if (window.closer() != window.ok())
       return;
 
-    name = window->findChild("name")->text();
+    name = window.name()->text();
   }
 
+  LayerGroup* parent = sprite->root();
   Layer* activeLayer = writer.layer();
+  SelectedLayers selLayers = writer.site()->selectedLayers();
+  if (activeLayer) {
+    if (activeLayer->isGroup() &&
+        activeLayer->isExpanded() &&
+        !m_group) {
+      parent = static_cast<LayerGroup*>(activeLayer);
+      activeLayer = nullptr;
+    }
+    else {
+      parent = activeLayer->parent();
+    }
+  }
+
   Layer* layer;
   {
-    Transaction transaction(writer.context(), "New Layer");
+    Transaction transaction(
+      writer.context(),
+      std::string("New ") + layerPrefix());
     DocumentApi api = document->getApi(transaction);
-    layer = api.newLayer(sprite, name);
+
+    if (m_group)
+      layer = api.newGroup(parent, name);
+    else
+      layer = api.newLayer(parent, name);
+
+    ASSERT(layer->parent());
 
     // If "top" parameter is false, create the layer above the active
     // one.
-    if (activeLayer && !m_top)
-      api.restackLayerAfter(layer, activeLayer);
+    if (activeLayer && !m_top) {
+      api.restackLayerAfter(layer,
+                            activeLayer->parent(),
+                            activeLayer);
+
+      // Put all selected layers inside the group
+      if (m_group && writer.site()->inTimeline()) {
+        LayerGroup* commonParent = nullptr;
+        layer_t sameParents = 0;
+        for (Layer* l : selLayers) {
+          if (!commonParent ||
+              commonParent == l->parent()) {
+            commonParent = l->parent();
+            ++sameParents;
+          }
+        }
+
+        if (sameParents == selLayers.size()) {
+          for (Layer* newChild : selLayers.toLayerList()) {
+            transaction.execute(
+              new cmd::MoveLayer(newChild, layer,
+                                 static_cast<LayerGroup*>(layer)->lastLayer()));
+          }
+        }
+      }
+    }
 
     transaction.commit();
   }
   update_screen_for_document(document);
 
   StatusBar::instance()->invalidate();
-  StatusBar::instance()->showTip(1000, "Layer `%s' created", name.c_str());
+  StatusBar::instance()->showTip(
+    1000, "%s '%s' created",
+    layerPrefix(),
+    name.c_str());
 
   App::instance()->mainWindow()->popTimeline();
 }
 
-static std::string get_unique_layer_name(Sprite* sprite)
+std::string NewLayerCommand::getUniqueLayerName(const Sprite* sprite) const
 {
   char buf[1024];
-  std::sprintf(buf, "Layer %d", get_max_layer_num(sprite->folder())+1);
+  std::sprintf(buf, "%s %d",
+               layerPrefix(),
+               getMaxLayerNum(sprite->root())+1);
   return buf;
 }
 
-static int get_max_layer_num(Layer* layer)
+int NewLayerCommand::getMaxLayerNum(const Layer* layer) const
 {
+  std::string prefix = layerPrefix();
+  prefix += " ";
+
   int max = 0;
+  if (std::strncmp(layer->name().c_str(), prefix.c_str(), prefix.size()) == 0)
+    max = std::strtol(layer->name().c_str()+prefix.size(), NULL, 10);
 
-  if (std::strncmp(layer->name().c_str(), "Layer ", 6) == 0)
-    max = std::strtol(layer->name().c_str()+6, NULL, 10);
-
-  if (layer->isFolder()) {
-    LayerIterator it = static_cast<LayerFolder*>(layer)->getLayerBegin();
-    LayerIterator end = static_cast<LayerFolder*>(layer)->getLayerEnd();
-
-    for (; it != end; ++it) {
-      int tmp = get_max_layer_num(*it);
+  if (layer->isGroup()) {
+    for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers()) {
+      int tmp = getMaxLayerNum(child);
       max = MAX(tmp, max);
     }
   }
@@ -151,6 +205,11 @@ static int get_max_layer_num(Layer* layer)
   return max;
 }
 
+const char* NewLayerCommand::layerPrefix() const
+{
+  return (m_group ? "Group": "Layer");
+}
+
 Command* CommandFactory::createNewLayerCommand()
 {
   return new NewLayerCommand;
diff --git a/src/app/commands/cmd_new_layer_set.cpp b/src/app/commands/cmd_new_layer_set.cpp
deleted file mode 100644
index f7c257acb..000000000
--- a/src/app/commands/cmd_new_layer_set.cpp
+++ /dev/null
@@ -1,87 +0,0 @@
-// Aseprite
-// Copyright (C) 2001-2015  David Capello
-//
-// This program is free software; you can redistribute it and/or modify
-// it under the terms of the GNU General Public License version 2 as
-// published by the Free Software Foundation.
-
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include "app/app.h"
-#include "app/commands/command.h"
-#include "app/context_access.h"
-#include "app/document_api.h"
-#include "app/document_api.h"
-#include "app/find_widget.h"
-#include "app/load_widget.h"
-#include "app/modules/gui.h"
-#include "app/ui/status_bar.h"
-#include "app/transaction.h"
-#include "doc/layer.h"
-#include "doc/sprite.h"
-#include "ui/ui.h"
-
-namespace app {
-
-using namespace ui;
-
-class NewLayerSetCommand : public Command {
-public:
-  NewLayerSetCommand();
-  Command* clone() const override { return new NewLayerSetCommand(*this); }
-
-protected:
-  bool onEnabled(Context* context) override;
-  void onExecute(Context* context) override;
-};
-
-NewLayerSetCommand::NewLayerSetCommand()
-  : Command("NewLayerSet",
-            "New Layer Set",
-            CmdRecordableFlag)
-{
-}
-
-bool NewLayerSetCommand::onEnabled(Context* context)
-{
-  return context->checkFlags(ContextFlags::ActiveDocumentIsWritable |
-                             ContextFlags::HasActiveSprite);
-}
-
-void NewLayerSetCommand::onExecute(Context* context)
-{
-  ContextWriter writer(context);
-  Document* document(writer.document());
-  Sprite* sprite(writer.sprite());
-
-  // load the window widget
-  base::UniquePtr<Window> window(app::load_widget<Window>("new_layer.xml", "new_layer_set"));
-
-  window->openWindowInForeground();
-
-  if (window->closer() != window->findChild("ok"))
-    return;
-
-  std::string name = window->findChild("name")->text();
-  Layer* layer;
-  {
-    Transaction transaction(writer.context(), "New Layer");
-    layer = document->getApi(transaction).newLayerFolder(sprite);
-    transaction.commit();
-  }
-  layer->setName(name);
-
-  update_screen_for_document(document);
-
-  StatusBar::instance()->invalidate();
-  StatusBar::instance()->showTip(1000, "Layer `%s' created", name.c_str());
-}
-
-Command* CommandFactory::createNewLayerSetCommand()
-{
-  return new NewLayerSetCommand;
-}
-
-} // namespace app
diff --git a/src/app/commands/cmd_new_sprite_from_selection.cpp b/src/app/commands/cmd_new_sprite_from_selection.cpp
index 4f3ca31fd..43109fb30 100644
--- a/src/app/commands/cmd_new_sprite_from_selection.cpp
+++ b/src/app/commands/cmd_new_sprite_from_selection.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -72,7 +72,7 @@ void NewSpriteFromSelectionCommand::onExecute(Context* context)
 
   palette->copyColorsTo(dstSprite->palette(frame_t(0)));
 
-  LayerImage* dstLayer = static_cast<LayerImage*>(dstSprite->folder()->getFirstLayer());
+  LayerImage* dstLayer = static_cast<LayerImage*>(dstSprite->root()->firstLayer());
   if (site.layer()->isBackground())
     dstLayer->configureAsBackground(); // Configure layer name as background
   dstLayer->setFlags(site.layer()->flags()); // Copy all flags
diff --git a/src/app/commands/cmd_remove_frame.cpp b/src/app/commands/cmd_remove_frame.cpp
index 81554bffb..0448d96a2 100644
--- a/src/app/commands/cmd_remove_frame.cpp
+++ b/src/app/commands/cmd_remove_frame.cpp
@@ -14,7 +14,6 @@
 #include "app/context_access.h"
 #include "app/document_api.h"
 #include "app/modules/gui.h"
-#include "app/ui/timeline.h"
 #include "app/transaction.h"
 #include "doc/sprite.h"
 #include "ui/ui.h"
@@ -55,14 +54,10 @@ void RemoveFrameCommand::onExecute(Context* context)
   {
     Transaction transaction(writer.context(), "Remove Frame");
     DocumentApi api = document->getApi(transaction);
-
-    // TODO the range of selected frames should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    if (range.enabled()) {
-      for (frame_t frame = range.frameEnd(),
-             begin = range.frameBegin()-1;
-           frame != begin;
-           --frame) {
+    const Site* site = writer.site();
+    if (site->inTimeline() &&
+        !site->selectedFrames().empty()) {
+      for (frame_t frame : site->selectedFrames().reversed()) {
         api.removeFrame(sprite, frame);
       }
     }
diff --git a/src/app/commands/cmd_remove_layer.cpp b/src/app/commands/cmd_remove_layer.cpp
index 5b82c1c20..9cb12d210 100644
--- a/src/app/commands/cmd_remove_layer.cpp
+++ b/src/app/commands/cmd_remove_layer.cpp
@@ -15,7 +15,6 @@
 #include "app/document_api.h"
 #include "app/modules/gui.h"
 #include "app/ui/status_bar.h"
-#include "app/ui/timeline.h"
 #include "app/transaction.h"
 #include "doc/layer.h"
 #include "doc/sprite.h"
@@ -52,34 +51,43 @@ bool RemoveLayerCommand::onEnabled(Context* context)
 
 void RemoveLayerCommand::onExecute(Context* context)
 {
-  std::string layer_name;
+  std::string layerName;
   ContextWriter writer(context);
   Document* document(writer.document());
   Sprite* sprite(writer.sprite());
-  Layer* layer(writer.layer());
   {
     Transaction transaction(writer.context(), "Remove Layer");
     DocumentApi api = document->getApi(transaction);
 
-    // TODO the range of selected layer should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    if (range.enabled()) {
-      if (range.layers() == sprite->countLayers()) {
+    const Site* site = writer.site();
+    if (site->inTimeline() &&
+        !site->selectedLayers().empty()) {
+      SelectedLayers selLayers = site->selectedLayers();
+      selLayers.removeChildrenIfParentIsSelected();
+
+      layer_t deletedTopLevelLayers = 0;
+      for (Layer* layer : selLayers) {
+        if (layer->parent() == sprite->root())
+          ++deletedTopLevelLayers;
+      }
+
+      if (deletedTopLevelLayers == sprite->root()->layersCount()) {
         ui::Alert::show("Error<<You cannot delete all layers.||&OK");
         return;
       }
 
-      for (LayerIndex layer = range.layerEnd(); layer >= range.layerBegin(); --layer) {
-        api.removeLayer(sprite->indexToLayer(layer));
+      for (Layer* layer : selLayers) {
+        api.removeLayer(layer);
       }
     }
     else {
-      if (sprite->countLayers() == 1) {
+      if (sprite->allLayersCount() == 1) {
         ui::Alert::show("Error<<You cannot delete the last layer.||&OK");
         return;
       }
 
-      layer_name = layer->name();
+      Layer* layer = writer.layer();
+      layerName = layer->name();
       api.removeLayer(layer);
     }
 
@@ -88,8 +96,8 @@ void RemoveLayerCommand::onExecute(Context* context)
   update_screen_for_document(document);
 
   StatusBar::instance()->invalidate();
-  if (!layer_name.empty())
-    StatusBar::instance()->showTip(1000, "Layer `%s' removed", layer_name.c_str());
+  if (!layerName.empty())
+    StatusBar::instance()->showTip(1000, "Layer '%s' removed", layerName.c_str());
   else
     StatusBar::instance()->showTip(1000, "Layers removed");
 }
diff --git a/src/app/commands/cmd_set_loop_section.cpp b/src/app/commands/cmd_set_loop_section.cpp
index 9d20f81b1..f3266bec5 100644
--- a/src/app/commands/cmd_set_loop_section.cpp
+++ b/src/app/commands/cmd_set_loop_section.cpp
@@ -85,8 +85,8 @@ void SetLoopSectionCommand::onExecute(Context* ctx)
     case Action::Auto: {
       auto range = App::instance()->timeline()->range();
       if (range.enabled() && (range.frames() > 1)) {
-        begin = range.frameBegin();
-        end = range.frameEnd();
+        begin = range.selectedFrames().firstFrame();
+        end = range.selectedFrames().lastFrame();
         on = true;
       }
       else {
diff --git a/src/app/commands/cmd_undo.cpp b/src/app/commands/cmd_undo.cpp
index 87eaf9bca..d61453f1b 100644
--- a/src/app/commands/cmd_undo.cpp
+++ b/src/app/commands/cmd_undo.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -71,7 +71,7 @@ void UndoCommand::onExecute(Context* context)
     Preferences::instance().undo.gotoModified();
 
   if (gotoModified) {
-    SpritePosition currentPosition(writer.site()->layerIndex(),
+    SpritePosition currentPosition(writer.site()->layer(),
                                    writer.site()->frame());
 
     if (m_type == Undo)
@@ -80,7 +80,9 @@ void UndoCommand::onExecute(Context* context)
       spritePosition = undo->nextRedoSpritePosition();
 
     if (spritePosition != currentPosition) {
-      current_editor->setLayer(sprite->indexToLayer(spritePosition.layerIndex()));
+      Layer* selectLayer = spritePosition.layer();
+      if (selectLayer)
+        current_editor->setLayer(selectLayer);
       current_editor->setFrame(spritePosition.frame());
 
       // Draw the current layer/frame (which is not undone yet) so the
@@ -112,11 +114,13 @@ void UndoCommand::onExecute(Context* context)
   // weren't able to reach before the undo).
   if (gotoModified) {
     SpritePosition currentPosition(
-      writer.site()->layerIndex(),
+      writer.site()->layer(),
       writer.site()->frame());
 
     if (spritePosition != currentPosition) {
-      current_editor->setLayer(sprite->indexToLayer(spritePosition.layerIndex()));
+      Layer* selectLayer = spritePosition.layer();
+      if (selectLayer)
+        current_editor->setLayer(selectLayer);
       current_editor->setFrame(spritePosition.frame());
     }
   }
diff --git a/src/app/commands/cmd_unlink_cel.cpp b/src/app/commands/cmd_unlink_cel.cpp
index 274c4a11d..ea6b981a0 100644
--- a/src/app/commands/cmd_unlink_cel.cpp
+++ b/src/app/commands/cmd_unlink_cel.cpp
@@ -16,7 +16,6 @@
 #include "app/modules/gui.h"
 #include "app/transaction.h"
 #include "app/ui/status_bar.h"
-#include "app/ui/timeline.h"
 #include "doc/cel.h"
 #include "doc/layer.h"
 #include "doc/sprite.h"
@@ -53,36 +52,31 @@ void UnlinkCelCommand::onExecute(Context* context)
   {
     Transaction transaction(writer.context(), "Unlink Cel");
 
-    // TODO the range of selected frames should be in doc::Site.
-    auto range = App::instance()->timeline()->range();
-    if (range.enabled()) {
-      Sprite* sprite = writer.sprite();
-
-      for (LayerIndex layerIdx = range.layerBegin(); layerIdx <= range.layerEnd(); ++layerIdx) {
-        Layer* layer = sprite->indexToLayer(layerIdx);
+    const Site* site = writer.site();
+    if (site->inTimeline() &&
+        !site->selectedLayers().empty()) {
+      for (Layer* layer : site->selectedLayers()) {
         if (!layer->isImage())
           continue;
 
+        if (!layer->isEditableHierarchy()) {
+          nonEditableLayers = true;
+          continue;
+        }
+
         LayerImage* layerImage = static_cast<LayerImage*>(layer);
 
-        for (frame_t frame = range.frameEnd(),
-               begin = range.frameBegin()-1;
-             frame != begin;
-             --frame) {
+        for (frame_t frame : site->selectedFrames().reversed()) {
           Cel* cel = layerImage->cel(frame);
-          if (cel && cel->links()) {
-            if (layerImage->isEditable())
-              transaction.execute(new cmd::UnlinkCel(cel));
-            else
-              nonEditableLayers = true;
-          }
+          if (cel && cel->links())
+            transaction.execute(new cmd::UnlinkCel(cel));
         }
       }
     }
     else {
       Cel* cel = writer.cel();
       if (cel && cel->links()) {
-        if (cel->layer()->isEditable())
+        if (cel->layer()->isEditableHierarchy())
           transaction.execute(new cmd::UnlinkCel(writer.cel()));
         else
           nonEditableLayers = true;
diff --git a/src/app/commands/commands_list.h b/src/app/commands/commands_list.h
index 3447df22b..fd58521b5 100644
--- a/src/app/commands/commands_list.h
+++ b/src/app/commands/commands_list.h
@@ -79,7 +79,6 @@ FOR_EACH_COMMAND(NewFile)
 FOR_EACH_COMMAND(NewFrame)
 FOR_EACH_COMMAND(NewFrameTag)
 FOR_EACH_COMMAND(NewLayer)
-FOR_EACH_COMMAND(NewLayerSet)
 FOR_EACH_COMMAND(NewSpriteFromSelection)
 FOR_EACH_COMMAND(OpenFile)
 FOR_EACH_COMMAND(OpenInFolder)
diff --git a/src/app/commands/filters/filter_manager_impl.cpp b/src/app/commands/filters/filter_manager_impl.cpp
index ce6eb4d56..8e5938e59 100644
--- a/src/app/commands/filters/filter_manager_impl.cpp
+++ b/src/app/commands/filters/filter_manager_impl.cpp
@@ -205,7 +205,7 @@ void FilterManagerImpl::applyToTarget()
   bool cancelled = false;
 
   ImagesCollector images((m_target & TARGET_ALL_LAYERS ?
-                          m_site.sprite()->folder():
+                          m_site.sprite()->root():
                           m_site.layer()),
                          m_site.frame(),
                          (m_target & TARGET_ALL_FRAMES) == TARGET_ALL_FRAMES,
diff --git a/src/app/context_flags.cpp b/src/app/context_flags.cpp
index 36acd9c9d..8f5f65ece 100644
--- a/src/app/context_flags.cpp
+++ b/src/app/context_flags.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -88,10 +88,10 @@ void ContextFlags::updateFlagsFromSite(const Site& site)
   if (layer->isBackground())
     m_flags |= ActiveLayerIsBackground;
 
-  if (layer->isVisible())
+  if (layer->isVisibleHierarchy())
     m_flags |= ActiveLayerIsVisible;
 
-  if (layer->isEditable())
+  if (layer->isEditableHierarchy())
     m_flags |= ActiveLayerIsEditable;
 
   if (layer->isImage()) {
diff --git a/src/app/crash/data_recovery.cpp b/src/app/crash/data_recovery.cpp
index 0c1d47119..98311a6df 100644
--- a/src/app/crash/data_recovery.cpp
+++ b/src/app/crash/data_recovery.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -38,7 +38,10 @@ DataRecovery::DataRecovery(doc::Context* ctx)
 
       SessionPtr session(new Session(itempath));
       if (!session->isRunning()) {
-        if (!session->isEmpty()) {
+        if (session->version() != VERSION) {
+          TRACE("cannot be loaded (incompatible version)\n");
+        }
+        else if (!session->isEmpty()) {
           TRACE("to be loaded\n");
           m_sessions.push_back(session);
         }
diff --git a/src/app/crash/read_document.cpp b/src/app/crash/read_document.cpp
index 5e4c096fc..c48eeea4b 100644
--- a/src/app/crash/read_document.cpp
+++ b/src/app/crash/read_document.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -240,11 +240,26 @@ private:
     // Read layers
     int nlayers = read32(s);
     if (nlayers >= 1 && nlayers < 0xfffff) {
+      std::map<ObjectId, LayerGroup*> layersMap;
+      layersMap[0] = spr->root(); // parentId = 0 is the root level
+
       for (int i = 0; i < nlayers; ++i) {
         ObjectId layId = read32(s);
+        ObjectId parentId = read32(s);
+
+        if (!layersMap[parentId]) {
+          Console().printf("Inexistent parent #%d for layer #%d", parentId, layId);
+          // Put this layer at the root level
+          parentId = 0;
+        }
+
         Layer* lay = loadObject<Layer*>("lay", layId, &Reader::readLayer);
-        if (lay)
-          spr->folder()->addLayer(lay);
+        if (lay) {
+          if (lay->isGroup())
+            layersMap[layId] = static_cast<LayerGroup*>(lay);
+
+          layersMap[parentId]->addLayer(lay);
+        }
       }
     }
     else {
@@ -279,7 +294,8 @@ private:
   Layer* readLayer(std::ifstream& s) {
     LayerFlags flags = (LayerFlags)read32(s);
     ObjectType type = (ObjectType)read16(s);
-    ASSERT(type == ObjectType::LayerImage);
+    ASSERT(type == ObjectType::LayerImage ||
+           type == ObjectType::LayerGroup);
 
     std::string name = read_string(s);
 
@@ -303,6 +319,12 @@ private:
       }
       return lay.release();
     }
+    else if (type == ObjectType::LayerGroup) {
+      base::UniquePtr<LayerGroup> lay(new LayerGroup(m_sprite));
+      lay->setName(name);
+      lay->setFlags(flags);
+      return lay.release();
+    }
     else {
       Console().printf("Unable to load layer named '%s', type #%d\n",
         name.c_str(), (int)type);
@@ -396,7 +418,7 @@ app::Document* read_document_with_raw_images(const std::string& dir,
 
   // Load each image as a new frame
   auto lay = new LayerImage(spr);
-  spr->folder()->addLayer(lay);
+  spr->root()->addLayer(lay);
 
   frame_t frame = 0;
   for (const auto& fn : base::list_files(dir)) {
@@ -421,7 +443,7 @@ app::Document* read_document_with_raw_images(const std::string& dir,
         break;
       case RawImagesAs::kLayers:
         lay = new LayerImage(spr);
-        spr->folder()->addLayer(lay);
+        spr->root()->addLayer(lay);
         break;
     }
   }
diff --git a/src/app/crash/session.cpp b/src/app/crash/session.cpp
index eb377e358..d773998d3 100644
--- a/src/app/crash/session.cpp
+++ b/src/app/crash/session.cpp
@@ -72,6 +72,19 @@ std::string Session::name() const
     return name;
 }
 
+std::string Session::version()
+{
+  if (m_version.empty()) {
+    std::string verfile = verFilename();
+    if (base::is_file(verfile)) {
+      std::ifstream pf(FSTREAM_PATH(verfile));
+      if (pf)
+        pf >> m_version;
+    }
+  }
+  return m_version;
+}
+
 const Session::Backups& Session::backups()
 {
   if (m_backups.empty()) {
diff --git a/src/app/crash/session.h b/src/app/crash/session.h
index ec97529d4..fdd9fb26d 100644
--- a/src/app/crash/session.h
+++ b/src/app/crash/session.h
@@ -41,6 +41,7 @@ namespace crash {
     ~Session();
 
     std::string name() const;
+    std::string version();
     const Backups& backups();
 
     bool isRunning();
@@ -65,8 +66,7 @@ namespace crash {
 
     base::pid m_pid;
     std::string m_path;
-    std::fstream m_log;
-    std::fstream m_pidFile;
+    std::string m_version;
     Backups m_backups;
 
     DISABLE_COPYING(Session);
diff --git a/src/app/crash/write_document.cpp b/src/app/crash/write_document.cpp
index d7bc06daf..63abd98ac 100644
--- a/src/app/crash/write_document.cpp
+++ b/src/app/crash/write_document.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -76,8 +76,8 @@ public:
     for (Cel* cel : spr->cels())
       saveObject("cel", cel, &Writer::writeCel);
 
-    std::vector<Layer*> layers;
-    spr->getLayersList(layers);
+    // Save all layers (top level, groups, children, etc.)
+    LayerList layers = spr->allLayers();
     for (Layer* lay : layers)
       saveObject("lay", lay, &Writer::writeLayerStructure);
 
@@ -104,11 +104,8 @@ private:
       write32(s, spr->frameDuration(fr));
 
     // IDs of all main layers
-    std::vector<Layer*> layers;
-    spr->getLayersList(layers);
-    write32(s, layers.size());
-    for (Layer* lay : layers)
-      write32(s, lay->id());
+    write32(s, spr->allLayersCount());
+    writeAllLayersID(s, 0, spr->root());
 
     // IDs of all palettes
     write32(s, spr->getPalettes().size());
@@ -121,21 +118,40 @@ private:
       write32(s, frtag->id());
   }
 
+  void writeAllLayersID(std::ofstream& s, ObjectId parentId, const LayerGroup* group) {
+    for (const Layer* lay : group->layers()) {
+      write32(s, lay->id());
+      write32(s, parentId);
+
+      if (lay->isGroup())
+        writeAllLayersID(s, lay->id(), static_cast<const LayerGroup*>(lay));
+    }
+  }
+
   void writeLayerStructure(std::ofstream& s, Layer* lay) {
     write32(s, static_cast<int>(lay->flags())); // Flags
     write16(s, static_cast<int>(lay->type()));  // Type
     write_string(s, lay->name());
 
-    if (lay->type() == ObjectType::LayerImage) {
-      CelConstIterator it, begin = static_cast<const LayerImage*>(lay)->getCelBegin();
-      CelConstIterator end = static_cast<const LayerImage*>(lay)->getCelEnd();
+    switch (lay->type()) {
 
-      // Cels
-      write32(s, static_cast<const LayerImage*>(lay)->getCelsCount());
-      for (it=begin; it != end; ++it) {
-        const Cel* cel = *it;
-        write32(s, cel->id());
+      case ObjectType::LayerImage: {
+        CelConstIterator it, begin = static_cast<const LayerImage*>(lay)->getCelBegin();
+        CelConstIterator end = static_cast<const LayerImage*>(lay)->getCelEnd();
+
+        // Cels
+        write32(s, static_cast<const LayerImage*>(lay)->getCelsCount());
+        for (it=begin; it != end; ++it) {
+          const Cel* cel = *it;
+          write32(s, cel->id());
+        }
+        break;
       }
+
+      case ObjectType::LayerGroup:
+        // Do nothing (the layer parent/children structure is saved in
+        // writeSprite/writeAllLayersID() functions)
+        break;
     }
   }
 
diff --git a/src/app/document.cpp b/src/app/document.cpp
index 57d40523c..dbabd6da5 100644
--- a/src/app/document.cpp
+++ b/src/app/document.cpp
@@ -324,23 +324,19 @@ void Document::copyLayerContent(const Layer* sourceLayer0, Document* destDoc, La
       newCel.release();
     }
   }
-  else if (sourceLayer0->isFolder() && destLayer0->isFolder()) {
-    const LayerFolder* sourceLayer = static_cast<const LayerFolder*>(sourceLayer0);
-    LayerFolder* destLayer = static_cast<LayerFolder*>(destLayer0);
+  else if (sourceLayer0->isGroup() && destLayer0->isGroup()) {
+    const LayerGroup* sourceLayer = static_cast<const LayerGroup*>(sourceLayer0);
+    LayerGroup* destLayer = static_cast<LayerGroup*>(destLayer0);
 
-    LayerConstIterator it = sourceLayer->getLayerBegin();
-    LayerConstIterator end = sourceLayer->getLayerEnd();
-
-    for (; it != end; ++it) {
-      Layer* sourceChild = *it;
+    for (Layer* sourceChild : sourceLayer->layers()) {
       base::UniquePtr<Layer> destChild(NULL);
 
       if (sourceChild->isImage()) {
         destChild.reset(new LayerImage(destLayer->sprite()));
         copyLayerContent(sourceChild, destDoc, destChild);
       }
-      else if (sourceChild->isFolder()) {
-        destChild.reset(new LayerFolder(destLayer->sprite()));
+      else if (sourceChild->isGroup()) {
+        destChild.reset(new LayerGroup(destLayer->sprite()));
         copyLayerContent(sourceChild, destDoc, destChild);
       }
       else {
@@ -352,7 +348,7 @@ void Document::copyLayerContent(const Layer* sourceLayer0, Document* destDoc, La
       // Add the new layer in the sprite.
 
       Layer* newLayer = destChild.release();
-      Layer* afterThis = destLayer->getLastLayer();
+      Layer* afterThis = destLayer->lastLayer();
 
       destLayer->addLayer(newLayer);
       destChild.release();
@@ -400,8 +396,8 @@ Document* Document::duplicate(DuplicateType type) const
   switch (type) {
 
     case DuplicateExactCopy:
-      // Copy the layer folder
-      copyLayerContent(sourceSprite->folder(), documentCopy, spriteCopy->folder());
+      // Copy the layer group
+      copyLayerContent(sourceSprite->root(), documentCopy, spriteCopy->root());
 
       ASSERT((spriteCopy->backgroundLayer() && sourceSprite->backgroundLayer()) ||
              (!spriteCopy->backgroundLayer() && !sourceSprite->backgroundLayer()));
@@ -410,16 +406,16 @@ Document* Document::duplicate(DuplicateType type) const
     case DuplicateWithFlattenLayers:
       {
         // Flatten layers
-        ASSERT(sourceSprite->folder() != NULL);
+        ASSERT(sourceSprite->root() != NULL);
 
         LayerImage* flatLayer = create_flatten_layer_copy
             (spriteCopy,
-             sourceSprite->folder(),
+             sourceSprite->root(),
              gfx::Rect(0, 0, sourceSprite->width(), sourceSprite->height()),
              frame_t(0), sourceSprite->lastFrame());
 
         // Add and select the new flat layer
-        spriteCopy->folder()->addLayer(flatLayer);
+        spriteCopy->root()->addLayer(flatLayer);
 
         // Configure the layer as background only if the original
         // sprite has a background layer.
diff --git a/src/app/document_api.cpp b/src/app/document_api.cpp
index 0d617dafa..ab9b335a7 100644
--- a/src/app/document_api.cpp
+++ b/src/app/document_api.cpp
@@ -82,8 +82,7 @@ void DocumentApi::cropSprite(Sprite* sprite, const gfx::Rect& bounds)
   setSpriteSize(sprite, bounds.w, bounds.h);
 
   app::Document* doc = static_cast<app::Document*>(sprite->document());
-  std::vector<Layer*> layers;
-  sprite->getLayersList(layers);
+  LayerList layers = sprite->allLayers();
   for (Layer* layer : layers) {
     if (!layer->isImage())
       continue;
@@ -238,7 +237,7 @@ void DocumentApi::moveFrame(Sprite* sprite, frame_t frame, frame_t beforeFrame)
     adjustFrameTags(sprite, beforeFrame, +1, true);
 
     // Change cel positions.
-    moveFrameLayer(sprite->folder(), frame, beforeFrame);
+    moveFrameLayer(sprite->root(), frame, beforeFrame);
   }
 }
 
@@ -289,12 +288,9 @@ void DocumentApi::moveFrameLayer(Layer* layer, frame_t frame, frame_t beforeFram
       break;
     }
 
-    case ObjectType::LayerFolder: {
-      LayerIterator it = static_cast<LayerFolder*>(layer)->getLayerBegin();
-      LayerIterator end = static_cast<LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it)
-        moveFrameLayer(*it, frame, beforeFrame);
+    case ObjectType::LayerGroup: {
+      for (Layer* child : static_cast<LayerGroup*>(layer)->layers())
+        moveFrameLayer(child, frame, beforeFrame);
       break;
     }
 
@@ -396,30 +392,27 @@ void DocumentApi::swapCel(
   if (cel2) setCelFramePosition(cel2, frame1);
 }
 
-LayerImage* DocumentApi::newLayer(Sprite* sprite, const std::string& name)
+LayerImage* DocumentApi::newLayer(LayerGroup* parent, const std::string& name)
 {
-  LayerImage* layer = new LayerImage(sprite);
+  LayerImage* layer = new LayerImage(parent->sprite());
   layer->setName(name);
 
-  addLayer(sprite->folder(), layer,
-           sprite->folder()->getLastLayer());
-
+  addLayer(parent, layer, parent->lastLayer());
   return layer;
 }
 
-LayerFolder* DocumentApi::newLayerFolder(Sprite* sprite)
+LayerGroup* DocumentApi::newGroup(LayerGroup* parent, const std::string& name)
 {
-  LayerFolder* layer = new LayerFolder(sprite);
-
-  addLayer(sprite->folder(), layer,
-           sprite->folder()->getLastLayer());
+  LayerGroup* layer = new LayerGroup(parent->sprite());
+  layer->setName(name);
 
+  addLayer(parent, layer, parent->lastLayer());
   return layer;
 }
 
-void DocumentApi::addLayer(LayerFolder* folder, Layer* newLayer, Layer* afterThis)
+void DocumentApi::addLayer(LayerGroup* parent, Layer* newLayer, Layer* afterThis)
 {
-  m_transaction.execute(new cmd::AddLayer(folder, newLayer, afterThis));
+  m_transaction.execute(new cmd::AddLayer(parent, newLayer, afterThis));
 }
 
 void DocumentApi::removeLayer(Layer* layer)
@@ -429,17 +422,30 @@ void DocumentApi::removeLayer(Layer* layer)
   m_transaction.execute(new cmd::RemoveLayer(layer));
 }
 
-void DocumentApi::restackLayerAfter(Layer* layer, Layer* afterThis)
+void DocumentApi::restackLayerAfter(Layer* layer, LayerGroup* parent, Layer* afterThis)
 {
-  m_transaction.execute(new cmd::MoveLayer(layer, afterThis));
+  ASSERT(parent);
+
+  if (layer == afterThis)
+    return;
+
+  m_transaction.execute(new cmd::MoveLayer(layer, parent, afterThis));
 }
 
-void DocumentApi::restackLayerBefore(Layer* layer, Layer* beforeThis)
+void DocumentApi::restackLayerBefore(Layer* layer, LayerGroup* parent, Layer* beforeThis)
 {
-  LayerIndex beforeThisIdx = layer->sprite()->layerToIndex(beforeThis);
-  LayerIndex afterThisIdx = beforeThisIdx.previous();
+  ASSERT(parent);
 
-  restackLayerAfter(layer, layer->sprite()->indexToLayer(afterThisIdx));
+  if (layer == beforeThis)
+    return;
+
+  Layer* afterThis;
+  if (beforeThis)
+    afterThis = beforeThis->getPrevious();
+  else
+    afterThis = parent->lastLayer();
+
+  restackLayerAfter(layer, parent, afterThis);
 }
 
 void DocumentApi::backgroundFromLayer(Layer* layer)
@@ -457,26 +463,36 @@ void DocumentApi::flattenLayers(Sprite* sprite)
   m_transaction.execute(new cmd::FlattenLayers(sprite));
 }
 
-void DocumentApi::duplicateLayerAfter(Layer* sourceLayer, Layer* afterLayer)
+Layer* DocumentApi::duplicateLayerAfter(Layer* sourceLayer, LayerGroup* parent, Layer* afterLayer)
 {
-  base::UniquePtr<LayerImage> newLayerPtr(new LayerImage(sourceLayer->sprite()));
+  ASSERT(parent);
+  base::UniquePtr<Layer> newLayerPtr;
+
+  if (sourceLayer->isImage())
+    newLayerPtr.reset(new LayerImage(sourceLayer->sprite()));
+  else if (sourceLayer->isGroup())
+    newLayerPtr.reset(new LayerGroup(sourceLayer->sprite()));
+  else
+    throw std::runtime_error("Invalid layer type");
 
   m_document->copyLayerContent(sourceLayer, m_document, newLayerPtr);
 
   newLayerPtr->setName(newLayerPtr->name() + " Copy");
 
-  addLayer(sourceLayer->parent(), newLayerPtr, afterLayer);
+  addLayer(parent, newLayerPtr, afterLayer);
 
   // Release the pointer as it is owned by the sprite now.
-  newLayerPtr.release();
+  return newLayerPtr.release();
 }
 
-void DocumentApi::duplicateLayerBefore(Layer* sourceLayer, Layer* beforeLayer)
+Layer* DocumentApi::duplicateLayerBefore(Layer* sourceLayer, LayerGroup* parent, Layer* beforeLayer)
 {
-  LayerIndex beforeThisIdx = sourceLayer->sprite()->layerToIndex(beforeLayer);
-  LayerIndex afterThisIdx = beforeThisIdx.previous();
-
-  duplicateLayerAfter(sourceLayer, sourceLayer->sprite()->indexToLayer(afterThisIdx));
+  ASSERT(parent);
+  Layer* afterThis = (beforeLayer ? beforeLayer->getPreviousInWholeHierarchy(): nullptr);
+  Layer* newLayer = duplicateLayerAfter(sourceLayer, parent, afterThis);
+  if (newLayer)
+    restackLayerBefore(newLayer, parent, beforeLayer);
+  return newLayer;
 }
 
 Cel* DocumentApi::addCel(LayerImage* layer, frame_t frameNumber, const ImageRef& image)
diff --git a/src/app/document_api.h b/src/app/document_api.h
index 4d7b6d535..63cc29296 100644
--- a/src/app/document_api.h
+++ b/src/app/document_api.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -21,7 +21,7 @@ namespace doc {
   class Cel;
   class Image;
   class Layer;
-  class LayerFolder;
+  class LayerGroup;
   class LayerImage;
   class Mask;
   class Palette;
@@ -80,17 +80,17 @@ namespace app {
       LayerImage* layer, frame_t frame1, frame_t frame2);
 
     // Layers API
-    LayerImage* newLayer(Sprite* sprite, const std::string& name);
-    LayerFolder* newLayerFolder(Sprite* sprite);
-    void addLayer(LayerFolder* folder, Layer* newLayer, Layer* afterThis);
+    LayerImage* newLayer(LayerGroup* parent, const std::string& name);
+    LayerGroup* newGroup(LayerGroup* parent, const std::string& name);
+    void addLayer(LayerGroup* parent, Layer* newLayer, Layer* afterThis);
     void removeLayer(Layer* layer);
-    void restackLayerAfter(Layer* layer, Layer* afterThis);
-    void restackLayerBefore(Layer* layer, Layer* beforeThis);
+    void restackLayerAfter(Layer* layer, LayerGroup* parent, Layer* afterThis);
+    void restackLayerBefore(Layer* layer, LayerGroup* parent, Layer* beforeThis);
     void backgroundFromLayer(Layer* layer);
     void layerFromBackground(Layer* layer);
     void flattenLayers(Sprite* sprite);
-    void duplicateLayerAfter(Layer* sourceLayer, Layer* afterLayer);
-    void duplicateLayerBefore(Layer* sourceLayer, Layer* beforeLayer);
+    Layer* duplicateLayerAfter(Layer* sourceLayer, LayerGroup* parent, Layer* afterLayer);
+    Layer* duplicateLayerBefore(Layer* sourceLayer, LayerGroup* parent, Layer* beforeLayer);
 
     // Images API
     void replaceImage(Sprite* sprite, const ImageRef& oldImage, const ImageRef& newImage);
diff --git a/src/app/document_api_tests.cpp b/src/app/document_api_tests.cpp
index 56b852c31..a90a6de9f 100644
--- a/src/app/document_api_tests.cpp
+++ b/src/app/document_api_tests.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -22,13 +22,103 @@ using namespace doc;
 
 typedef base::UniquePtr<app::Document> DocumentPtr;
 
-TEST(DocumentApi, MoveCel) {
-  TestContextT<app::Context> ctx;
-  DocumentPtr doc(static_cast<app::Document*>(ctx.documents().add(32, 16)));
-  Sprite* sprite = doc->sprite();
-  LayerImage* layer1 = dynamic_cast<LayerImage*>(sprite->folder()->getFirstLayer());
-  LayerImage* layer2 = new LayerImage(sprite);
+class BasicDocApiTest : public ::testing::Test {
+public:
+  BasicDocApiTest() :
+    doc((static_cast<app::Document*>(ctx.documents().add(32, 16)))),
+    sprite(doc->sprite()),
+    root(sprite->root()),
+    layer1(dynamic_cast<LayerImage*>(sprite->root()->firstLayer())),
+    layer2(new LayerImage(sprite)),
+    layer3(new LayerImage(sprite))
+  {
+    root->addLayer(layer2);
+    root->addLayer(layer3);
+  }
 
+  ~BasicDocApiTest() {
+    doc->close();
+  }
+
+  TestContextT<app::Context> ctx;
+  DocumentPtr doc;
+  Sprite* sprite;
+  LayerGroup* root;
+  LayerImage* layer1;
+  LayerImage* layer2;
+  LayerImage* layer3;
+};
+
+TEST_F(BasicDocApiTest, RestackLayerBefore)
+{
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    // Do nothing
+    doc->getApi(transaction).restackLayerBefore(layer1, layer1->parent(), layer1);
+    EXPECT_EQ(layer1, root->firstLayer());
+    EXPECT_EQ(layer2, root->firstLayer()->getNext());
+    EXPECT_EQ(layer3, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    doc->getApi(transaction).restackLayerBefore(layer1, layer3->parent(), layer3);
+    EXPECT_EQ(layer2, root->firstLayer());
+    EXPECT_EQ(layer1, root->firstLayer()->getNext());
+    EXPECT_EQ(layer3, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    doc->getApi(transaction).restackLayerBefore(layer1, layer1->parent(), nullptr);
+    EXPECT_EQ(layer2, root->firstLayer());
+    EXPECT_EQ(layer3, root->firstLayer()->getNext());
+    EXPECT_EQ(layer1, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+}
+
+TEST_F(BasicDocApiTest, RestackLayerAfter)
+{
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    // Do nothing
+    doc->getApi(transaction).restackLayerAfter(layer1, layer1->parent(), layer1);
+    EXPECT_EQ(layer1, root->firstLayer());
+    EXPECT_EQ(layer2, root->firstLayer()->getNext());
+    EXPECT_EQ(layer3, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    doc->getApi(transaction).restackLayerAfter(layer1, layer3->parent(), layer3);
+    EXPECT_EQ(layer2, root->firstLayer());
+    EXPECT_EQ(layer3, root->firstLayer()->getNext());
+    EXPECT_EQ(layer1, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+
+  EXPECT_EQ(layer1, root->firstLayer());
+  {
+    Transaction transaction(&ctx, "");
+    doc->getApi(transaction).restackLayerAfter(layer3, layer3->parent(), nullptr);
+    EXPECT_EQ(layer3, root->firstLayer());
+    EXPECT_EQ(layer1, root->firstLayer()->getNext());
+    EXPECT_EQ(layer2, root->firstLayer()->getNext()->getNext());
+    // Rollback
+  }
+}
+
+TEST_F(BasicDocApiTest, MoveCel)
+{
   Cel* cel1 = layer1->cel(frame_t(0));
   cel1->setPosition(2, -2);
   cel1->setOpacity(128);
@@ -61,6 +151,4 @@ TEST(DocumentApi, MoveCel) {
   EXPECT_EQ(2, cel2->x());
   EXPECT_EQ(-2, cel2->y());
   EXPECT_EQ(128, cel2->opacity());
-
-  doc->close();
 }
diff --git a/src/app/document_exporter.cpp b/src/app/document_exporter.cpp
index 6f3c55115..0f1ee1f3b 100644
--- a/src/app/document_exporter.cpp
+++ b/src/app/document_exporter.cpp
@@ -396,7 +396,7 @@ Document* DocumentExporter::exportSheet()
     createEmptyTexture(samples));
 
   Sprite* texture = textureDocument->sprite();
-  Image* textureImage = texture->folder()->getFirstLayer()
+  Image* textureImage = texture->root()->firstLayer()
     ->cel(frame_t(0))->image();
 
   renderTexture(samples, textureImage);
@@ -758,10 +758,7 @@ void DocumentExporter::createDataFile(const Samples& samples, std::ostream& os,
       Document* doc = item.doc;
       Sprite* sprite = doc->sprite();
 
-      std::vector<Layer*> layers;
-      sprite->getLayersList(layers);
-
-      for (Layer* layer : layers) {
+      for (Layer* layer : sprite->allVisibleLayers()) {
         if (firstLayer)
           firstLayer = false;
         else
diff --git a/src/app/document_range.cpp b/src/app/document_range.cpp
index 59ab7fba1..4ccfbf3bf 100644
--- a/src/app/document_range.cpp
+++ b/src/app/document_range.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -22,103 +22,139 @@ using namespace doc;
 
 DocumentRange::DocumentRange()
   : m_type(kNone)
-  , m_layerBegin(0)
-  , m_layerEnd(-1)
-  , m_frameBegin(0)
-  , m_frameEnd(-1)
+  , m_selectingFromLayer(nullptr)
+  , m_selectingFromFrame(-1)
 {
 }
 
 DocumentRange::DocumentRange(Cel* cel)
   : m_type(kCels)
-  , m_layerBegin(cel->sprite()->layerToIndex(cel->layer()))
-  , m_layerEnd(m_layerBegin)
-  , m_frameBegin(cel->frame())
-  , m_frameEnd(m_frameBegin)
+  , m_selectingFromLayer(nullptr)
+  , m_selectingFromFrame(-1)
 {
+  m_selectedLayers.insert(cel->layer());
+  m_selectedFrames.insert(cel->frame());
 }
 
-void DocumentRange::startRange(LayerIndex layer, frame_t frame, Type type)
-{
-  m_type = type;
-  m_layerBegin = m_layerEnd = layer;
-  m_frameBegin = m_frameEnd = frame;
-}
-
-void DocumentRange::endRange(LayerIndex layer, frame_t frame)
-{
-  ASSERT(enabled());
-  m_layerEnd = layer;
-  m_frameEnd = frame;
-}
-
-void DocumentRange::disableRange()
+void DocumentRange::clearRange()
 {
   m_type = kNone;
+  m_selectedLayers.clear();
+  m_selectedFrames.clear();
 }
 
-bool DocumentRange::inRange(LayerIndex layer) const
+void DocumentRange::startRange(Layer* fromLayer, frame_t fromFrame, Type type)
+{
+  m_type = type;
+  m_selectingFromLayer = fromLayer;
+  m_selectingFromFrame = fromFrame;
+
+  if (fromLayer)
+    m_selectedLayers.insert(fromLayer);
+  if (fromFrame >= 0)
+    m_selectedFrames.insert(fromFrame);
+}
+
+void DocumentRange::endRange(Layer* toLayer, frame_t toFrame)
+{
+  ASSERT(enabled());
+
+  if (m_selectingFromLayer && toLayer)
+    selectLayerRange(m_selectingFromLayer, toLayer);
+
+  if (m_selectingFromFrame >= 0)
+    selectFrameRange(m_selectingFromFrame, toFrame);
+}
+
+bool DocumentRange::contains(Layer* layer) const
 {
   if (enabled())
-    return (layer >= layerBegin() && layer <= layerEnd());
+    return m_selectedLayers.contains(layer);
   else
     return false;
 }
 
-bool DocumentRange::inRange(frame_t frame) const
+void DocumentRange::displace(layer_t layerDelta, frame_t frameDelta)
 {
-  if (enabled())
-    return (frame >= frameBegin() && frame <= frameEnd());
-  else
-    return false;
+  m_selectedLayers.displace(layerDelta);
+  m_selectedFrames.displace(frameDelta);
 }
 
-bool DocumentRange::inRange(LayerIndex layer, frame_t frame) const
-{
-  return inRange(layer) && inRange(frame);
-}
-
-void DocumentRange::setLayers(int layers)
-{
-  if (m_layerBegin <= m_layerEnd) m_layerEnd = m_layerBegin + LayerIndex(layers - 1);
-  else m_layerBegin = m_layerEnd + LayerIndex(layers - 1);
-}
-
-void DocumentRange::setFrames(frame_t frames)
-{
-  if (m_frameBegin <= m_frameEnd)
-    m_frameEnd = (m_frameBegin + frames) - 1;
-  else
-    m_frameBegin = (m_frameEnd + frames) - 1;
-}
-
-void DocumentRange::displace(int layerDelta, int frameDelta)
-{
-  m_layerBegin += LayerIndex(layerDelta);
-  m_layerEnd   += LayerIndex(layerDelta);
-  m_frameBegin += frame_t(frameDelta);
-  m_frameEnd   += frame_t(frameDelta);
-}
-
-bool DocumentRange::convertToCels(Sprite* sprite)
+bool DocumentRange::convertToCels(const Sprite* sprite)
 {
   switch (m_type) {
     case DocumentRange::kNone:
       return false;
     case DocumentRange::kCels:
       break;
-    case DocumentRange::kFrames:
-      m_layerBegin = sprite->firstLayer();
-      m_layerEnd = sprite->lastLayer();
-      m_type = DocumentRange::kCels;
+    case DocumentRange::kFrames: {
+      LayerList layers = sprite->allBrowsableLayers();
+      ASSERT(layers.empty());
+      if (!layers.empty()) {
+        selectLayerRange(layers.front(), layers.back());
+        m_type = DocumentRange::kCels;
+      }
+      else
+        return false;
       break;
+    }
     case DocumentRange::kLayers:
-      m_frameBegin = frame_t(0);
-      m_frameEnd = sprite->lastFrame();
+      selectFrameRange(0, sprite->lastFrame());
       m_type = DocumentRange::kCels;
       break;
   }
   return true;
 }
 
+void DocumentRange::selectLayerRange(Layer* fromLayer, Layer* toLayer)
+{
+  ASSERT(fromLayer);
+  ASSERT(toLayer);
+
+  bool goNext = false;
+  bool goPrev = false;
+  Layer* it;
+
+  if (fromLayer != toLayer) {
+    it = m_selectingFromLayer;
+    while (it) {
+      if (it == toLayer) {
+        goNext = true;
+        break;
+      }
+      it = it->getNextInWholeHierarchy();
+    }
+
+    if (!goNext) {
+      it = m_selectingFromLayer;
+      while (it) {
+        if (it == toLayer) {
+          goPrev = true;
+          break;
+        }
+        it = it->getPreviousInWholeHierarchy();
+      }
+    }
+  }
+
+  it = m_selectingFromLayer;
+  do {
+    m_selectedLayers.insert(it);
+    if (it == toLayer)
+      break;
+
+    if (goNext)
+      it = it->getNextInWholeHierarchy();
+    else if (goPrev)
+      it = it->getPreviousInWholeHierarchy();
+    else
+      break;
+  } while (it);
+}
+
+void DocumentRange::selectFrameRange(frame_t fromFrame, frame_t toFrame)
+{
+  m_selectedFrames.insert(fromFrame, toFrame);
+}
+
 } // namespace app
diff --git a/src/app/document_range.h b/src/app/document_range.h
index 989f8b2f2..66b4e94f8 100644
--- a/src/app/document_range.h
+++ b/src/app/document_range.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -10,9 +10,8 @@
 #pragma once
 
 #include "doc/frame.h"
-#include "doc/layer_index.h"
-
-#include <algorithm>
+#include "doc/selected_frames.h"
+#include "doc/selected_layers.h"
 
 namespace doc {
   class Cel;
@@ -31,39 +30,47 @@ namespace app {
 
     Type type() const { return m_type; }
     bool enabled() const { return m_type != kNone; }
-    LayerIndex layerBegin() const  { return std::min(m_layerBegin, m_layerEnd); }
-    LayerIndex layerEnd() const    { return std::max(m_layerBegin, m_layerEnd); }
-    frame_t frameBegin() const { return std::min(m_frameBegin, m_frameEnd); }
-    frame_t frameEnd() const   { return std::max(m_frameBegin, m_frameEnd); }
+    layer_t layers() const { return int(m_selectedLayers.size()); }
+    frame_t frames() const { return int(m_selectedFrames.size()); }
+    const SelectedLayers& selectedLayers() const  { return m_selectedLayers; }
+    const SelectedFrames& selectedFrames() const  { return m_selectedFrames; }
 
-    int layers() const { return layerEnd() - layerBegin() + 1; }
-    frame_t frames() const { return frameEnd() - frameBegin() + 1; }
-    void setLayers(int layers);
-    void setFrames(frame_t frames);
-    void displace(int layerDelta, int frameDelta);
+    void displace(layer_t layerDelta, frame_t frameDelta);
 
-    bool inRange(LayerIndex layer) const;
-    bool inRange(frame_t frame) const;
-    bool inRange(LayerIndex layer, frame_t frame) const;
+    bool contains(Layer* layer) const;
 
-    void startRange(LayerIndex layer, frame_t frame, Type type);
-    void endRange(LayerIndex layer, frame_t frame);
-    void disableRange();
-
-    bool operator==(const DocumentRange& o) const {
-      return m_type == o.m_type &&
-        layerBegin() == o.layerBegin() && layerEnd() == o.layerEnd() &&
-        frameBegin() == o.frameBegin() && frameEnd() == o.frameEnd();
+    bool contains(frame_t frame) const {
+      return m_selectedFrames.contains(frame);
     }
 
-    bool convertToCels(Sprite* sprite);
+    bool contains(Layer* layer, frame_t frame) const {
+      return contains(layer) && contains(frame);
+    }
+
+    void clearRange();
+    void startRange(Layer* fromLayer, frame_t fromFrame, Type type);
+    void endRange(Layer* toLayer, frame_t toFrame);
+
+    frame_t firstFrame() const { return m_selectedFrames.firstFrame(); }
+    frame_t lastFrame() const { return m_selectedFrames.lastFrame(); }
+
+    bool operator==(const DocumentRange& o) const {
+      return (m_type == o.m_type &&
+              m_selectedLayers == o.m_selectedLayers &&
+              m_selectedFrames == o.m_selectedFrames);
+    }
+
+    bool convertToCels(const Sprite* sprite);
 
   private:
+    void selectLayerRange(Layer* fromLayer, Layer* toLayer);
+    void selectFrameRange(frame_t fromFrame, frame_t toFrame);
+
     Type m_type;
-    LayerIndex m_layerBegin;
-    LayerIndex m_layerEnd;
-    frame_t m_frameBegin;
-    frame_t m_frameEnd;
+    SelectedLayers m_selectedLayers;
+    SelectedFrames m_selectedFrames;
+    Layer* m_selectingFromLayer;
+    frame_t m_selectingFromFrame;
   };
 
 } // namespace app
diff --git a/src/app/document_range_ops.cpp b/src/app/document_range_ops.cpp
index 6c1ebe124..2b05e494d 100644
--- a/src/app/document_range_ops.cpp
+++ b/src/app/document_range_ops.cpp
@@ -5,13 +5,15 @@
 // it under the terms of the GNU General Public License version 2 as
 // published by the Free Software Foundation.
 
+// Uncomment this in case you want to debug range ops
+//#define TRACE_RANGE_OPS
+
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
 
 #include "app/document_range_ops.h"
 
-#include "app/app.h"            // TODO remove this dependency
 #include "app/context_access.h"
 #include "app/document_api.h"
 #include "app/document_range.h"
@@ -21,14 +23,172 @@
 
 #include <stdexcept>
 
+#ifdef TRACE_RANGE_OPS
+#include <iostream>
+#endif
+
 namespace app {
 
 enum Op { Move, Copy };
 
+template<typename T>
+static void move_or_copy_cels(
+  DocumentApi& api, Op op,
+  LayerList& srcLayers,
+  LayerList& dstLayers,
+  T& srcFrames,
+  T& dstFrames)
+{
+  ASSERT(srcLayers.size() == dstLayers.size());
+
+  for (layer_t i=0; i<srcLayers.size(); ++i) {
+    auto srcFrame = srcFrames.begin();
+    auto dstFrame = dstFrames.begin();
+    auto srcFrameEnd = srcFrames.end();
+    auto dstFrameEnd = dstFrames.end();
+
+    for (; srcFrame != srcFrameEnd &&
+           dstFrame != dstFrameEnd; ++srcFrame, ++dstFrame) {
+      if (i >= 0 && i < srcLayers.size() && srcLayers[i]->isImage()) {
+        LayerImage* srcLayer = static_cast<LayerImage*>(srcLayers[i]);
+
+        if (i < dstLayers.size() && dstLayers[i]->isImage()) {
+          LayerImage* srcLayer = static_cast<LayerImage*>(srcLayers[i]);
+          LayerImage* dstLayer = static_cast<LayerImage*>(dstLayers[i]);
+
+#ifdef TRACE_RANGE_OPS
+          std::clog << (op == Move ? "Moving": "Copying")
+                    << " cel " << srcLayer->name() << "[" << *srcFrame << "]"
+                    << " into " << dstLayer->name() << "[" << *dstFrame << "]\n";
+#endif
+
+          switch (op) {
+            case Move: api.moveCel(srcLayer, *srcFrame, dstLayer, *dstFrame); break;
+            case Copy: api.copyCel(srcLayer, *srcFrame, dstLayer, *dstFrame); break;
+          }
+        }
+        else if (op == Move) {
+          api.clearCel(srcLayer, *srcFrame);
+        }
+      }
+    }
+  }
+}
+
+template<typename T>
+static DocumentRange move_or_copy_frames(
+  DocumentApi& api, Op op,
+  Sprite* sprite,
+  T& srcFrames,
+  frame_t dstFrame)
+{
+#ifdef TRACE_RANGE_OPS
+  std::clog << "move_or_copy_frames frames[";
+  for (auto srcFrame : srcFrames) {
+    std::clog << srcFrame << ", ";
+  }
+  std::clog << "] => " << dstFrame << "\n";
+#endif
+
+  auto srcFrame = srcFrames.begin();
+  auto srcFrameEnd = srcFrames.end();
+  frame_t srcDelta = 0;
+  frame_t firstCopiedBlock = 0;
+
+  for (; srcFrame != srcFrameEnd; ++srcFrame) {
+    frame_t fromFrame = (*srcFrame)+srcDelta;
+
+    switch (op) {
+
+      case Move:
+        if ((*srcFrame) >= dstFrame) {
+          srcDelta = 0;
+          fromFrame = *srcFrame;
+        }
+        break;
+
+      case Copy:
+        if (fromFrame >= dstFrame-1 && firstCopiedBlock) {
+          srcDelta += firstCopiedBlock;
+          fromFrame += firstCopiedBlock;
+          firstCopiedBlock = 0;
+        }
+        break;
+    }
+
+#ifdef TRACE_RANGE_OPS
+    std::clog << " [";
+    for (frame_t i=0; i<=sprite->lastFrame(); ++i) {
+      std::clog << (sprite->frameDuration(i)-1);
+    }
+    std::clog << "] => "
+              << (op == Move ? "Move": "Copy")
+              << " " << (*srcFrame) << "+" << (srcDelta) << " -> " << dstFrame << " => ";
+#endif
+
+    switch (op) {
+
+      case Move:
+        api.moveFrame(sprite, fromFrame, dstFrame);
+
+        if (fromFrame < dstFrame-1) {
+          --srcDelta;
+        }
+        else if (fromFrame > dstFrame-1) {
+          ++dstFrame;
+        }
+        break;
+
+      case Copy:
+        api.copyFrame(sprite, fromFrame, dstFrame);
+
+        if (fromFrame < dstFrame-1) {
+          ++firstCopiedBlock;
+        }
+        else if (fromFrame >= dstFrame-1) {
+          ++srcDelta;
+        }
+        ++dstFrame;
+        break;
+    }
+
+#ifdef TRACE_RANGE_OPS
+    std::clog << " [";
+    for (frame_t i=0; i<=sprite->lastFrame(); ++i) {
+      std::clog << (sprite->frameDuration(i)-1);
+    }
+    std::clog << "]\n";
+#endif
+  }
+
+  DocumentRange result;
+  result.startRange(nullptr, dstFrame-srcFrames.size(), DocumentRange::kFrames);
+  result.endRange(nullptr, dstFrame-1);
+  return result;
+}
+
 static DocumentRange drop_range_op(
   Document* doc, Op op, const DocumentRange& from,
-  DocumentRangePlace place, const DocumentRange& to)
+  DocumentRangePlace place, DocumentRange to)
 {
+  // Convert "first child" operation into a insert after last child.
+  LayerGroup* parent = nullptr;
+  if (to.type() == DocumentRange::kLayers &&
+      !to.selectedLayers().empty()) {
+    if (place == kDocumentRangeFirstChild &&
+        (*to.selectedLayers().begin())->isGroup()) {
+      place = kDocumentRangeAfter;
+      parent = static_cast<LayerGroup*>((*to.selectedLayers().begin()));
+
+      to.clearRange();
+      to.startRange(parent->lastLayer(), -1, DocumentRange::kLayers);
+      to.endRange(parent->lastLayer(), -1);
+    }
+    else {
+      parent = (*to.selectedLayers().begin())->parent();
+    }
+  }
+
   if (place != kDocumentRangeBefore &&
       place != kDocumentRangeAfter) {
     ASSERT(false);
@@ -40,36 +200,69 @@ static DocumentRange drop_range_op(
   // Check noop/trivial/do nothing cases, i.e., move a range to the same place.
   // Also check invalid cases, like moving a Background layer.
   switch (from.type()) {
+
     case DocumentRange::kCels:
       if (from == to)
         return from;
       break;
+
     case DocumentRange::kFrames:
       if (op == Move) {
-        if ((to.frameBegin() >= from.frameBegin() && to.frameEnd() <= from.frameEnd()) ||
-            (place == kDocumentRangeBefore && to.frameBegin() == from.frameEnd()+1) ||
-            (place == kDocumentRangeAfter && to.frameEnd() == from.frameBegin()-1))
+        // Simple cases with one continuos range of frames that are a
+        // no-op.
+        if ((from.selectedFrames().ranges() == 1) &&
+            ((to.firstFrame() >= from.firstFrame() &&
+              to.lastFrame() <= from.lastFrame()) ||
+             (place == kDocumentRangeBefore && to.firstFrame() == from.lastFrame()+1) ||
+             (place == kDocumentRangeAfter && to.lastFrame() == from.firstFrame()-1)))
           return from;
       }
       break;
+
     case DocumentRange::kLayers:
       if (op == Move) {
-        if ((to.layerBegin() >= from.layerBegin() && to.layerEnd() <= from.layerEnd()) ||
-            (place == kDocumentRangeBefore && to.layerBegin() == from.layerEnd()+1) ||
-            (place == kDocumentRangeAfter && to.layerEnd() == from.layerBegin()-1))
+        SelectedLayers srcSelLayers = from.selectedLayers();
+        SelectedLayers dstSelLayers = to.selectedLayers();
+        LayerList srcLayers = srcSelLayers.toLayerList();
+        LayerList dstLayers = dstSelLayers.toLayerList();
+        ASSERT(!srcLayers.empty());
+        if (srcLayers.empty())
           return from;
 
+        // dstLayers can be nullptr when we insert the first child in
+        // a group.
+
+        // Check no-ops when we move layers at the same level (all
+        // layers with the same parent), all adjacents, and which are
+        // moved to the same place.
+        if (!dstSelLayers.empty() &&
+            srcSelLayers.hasSameParent() &&
+            dstSelLayers.hasSameParent() &&
+            are_layers_adjacent(srcLayers) &&
+            are_layers_adjacent(dstLayers)) {
+          for (Layer* srcLayer : srcLayers)
+            if (dstSelLayers.contains(srcLayer))
+              return from;
+
+          if ((place == kDocumentRangeBefore
+               && dstLayers.front() == srcLayers.back()->getNext()) ||
+              (place == kDocumentRangeAfter
+               && dstLayers.back() == srcLayers.front()->getPrevious()))
+            return from;
+        }
+
         // We cannot move the background
-        for (LayerIndex i = from.layerBegin(); i <= from.layerEnd(); ++i)
-          if (sprite->indexToLayer(i)->isBackground())
+        for (Layer* layer : srcSelLayers)
+          if (layer->isBackground())
             throw std::runtime_error("The background layer cannot be moved");
       }
 
       // Before background
       if (place == kDocumentRangeBefore) {
-        Layer* background = sprite->indexToLayer(to.layerBegin());
-        if (background && background->isBackground())
-          throw std::runtime_error("You cannot move or copy something below the background layer");
+        for (Layer* background : to.selectedLayers()) {
+          if (background && background->isBackground())
+            throw std::runtime_error("You cannot move or copy something below the background layer");
+        }
       }
       break;
   }
@@ -92,238 +285,122 @@ static DocumentRange drop_range_op(
     DocumentApi api = doc->getApi(transaction);
 
     // TODO Try to add the range with just one call to DocumentApi
-    // methods, to avoid generating a lot of SetCelFrame undoers (see
-    // DocumentApi::setCelFramePosition).
+    // methods, to avoid generating a lot of cmd::SetCelFrame (see
+    // DocumentApi::setCelFramePosition() function).
 
     switch (from.type()) {
 
-      case DocumentRange::kCels:
-        {
-          std::vector<Layer*> layers;
-          sprite->getLayersList(layers);
+      case DocumentRange::kCels: {
+        LayerList allLayers = sprite->allBrowsableLayers();
+        if (allLayers.empty())
+          break;
 
-          int srcLayerBegin, srcLayerStep, srcLayerEnd;
-          int dstLayerBegin, dstLayerStep;
-          frame_t srcFrameBegin, srcFrameStep, srcFrameEnd;
-          frame_t dstFrameBegin, dstFrameStep;
+        LayerList srcLayers = from.selectedLayers().toLayerList();
+        LayerList dstLayers = to.selectedLayers().toLayerList();
+        if (srcLayers.empty())
+          throw std::invalid_argument("You need to specify a non-empty cels range");
 
-          if (to.layerBegin() <= from.layerBegin()) {
-            srcLayerBegin = from.layerBegin();
-            srcLayerStep = 1;
-            srcLayerEnd = from.layerEnd()+1;
-            dstLayerBegin = to.layerBegin();
-            dstLayerStep = 1;
-          }
-          else {
-            srcLayerBegin = from.layerEnd();
-            srcLayerStep = -1;
-            srcLayerEnd = from.layerBegin()-1;
-            dstLayerBegin = to.layerEnd();
-            dstLayerStep = -1;
-          }
-
-          if (to.frameBegin() <= from.frameBegin()) {
-            srcFrameBegin = from.frameBegin();
-            srcFrameStep = frame_t(1);
-            srcFrameEnd = from.frameEnd()+1;
-            dstFrameBegin = to.frameBegin();
-            dstFrameStep = frame_t(1);
-          }
-          else {
-            srcFrameBegin = from.frameEnd();
-            srcFrameStep = frame_t(-1);
-            srcFrameEnd = from.frameBegin()-1;
-            dstFrameBegin = to.frameEnd();
-            dstFrameStep = frame_t(-1);
-          }
-
-          for (int srcLayerIdx = srcLayerBegin,
-                 dstLayerIdx = dstLayerBegin; srcLayerIdx != srcLayerEnd; ) {
-            for (frame_t srcFrame = srcFrameBegin,
-                   dstFrame = dstFrameBegin; srcFrame != srcFrameEnd; ) {
-              if (dstLayerIdx < 0 || dstLayerIdx >= int(layers.size()) ||
-                  srcLayerIdx < 0 || srcLayerIdx >= int(layers.size()))
-                break;
-
-              LayerImage* srcLayer = static_cast<LayerImage*>(layers[srcLayerIdx]);
-              LayerImage* dstLayer = static_cast<LayerImage*>(layers[dstLayerIdx]);
-
-              switch (op) {
-                case Move: api.moveCel(srcLayer, srcFrame, dstLayer, dstFrame); break;
-                case Copy: api.copyCel(srcLayer, srcFrame, dstLayer, dstFrame); break;
-              }
-
-              srcFrame += srcFrameStep;
-              dstFrame += dstFrameStep;
-            }
-            srcLayerIdx += srcLayerStep;
-            dstLayerIdx += dstLayerStep;
-          }
-
-          resultRange = to;
+        if (find_layer_index(allLayers, srcLayers.front()) <
+            find_layer_index(allLayers, dstLayers.front())) {
+          std::reverse(srcLayers.begin(), srcLayers.end());
+          std::reverse(dstLayers.begin(), dstLayers.end());
         }
-        break;
 
-      case DocumentRange::kFrames:
-        {
-          frame_t srcFrameBegin = 0, srcFrameStep, srcFrameEnd = 0;
-          frame_t dstFrameBegin = 0, dstFrameStep;
+        if (from.firstFrame() < to.firstFrame()) {
+          auto srcFrames = from.selectedFrames().reversed();
+          auto dstFrames = to.selectedFrames().reversed();
 
-          switch (op) {
-
-            case Move:
-              if (place == kDocumentRangeBefore) {
-                if (to.frameBegin() <= from.frameBegin()) {
-                  srcFrameBegin = from.frameBegin();
-                  srcFrameStep = frame_t(1);
-                  srcFrameEnd = from.frameEnd()+1;
-                  dstFrameBegin = to.frameBegin();
-                  dstFrameStep = frame_t(1);
-                }
-                else {
-                  srcFrameBegin = from.frameEnd();
-                  srcFrameStep = frame_t(-1);
-                  srcFrameEnd = from.frameBegin()-1;
-                  dstFrameBegin = to.frameBegin();
-                  dstFrameStep = frame_t(-1);
-                }
-              }
-              else if (place == kDocumentRangeAfter) {
-                if (to.frameEnd() <= from.frameBegin()) {
-                  srcFrameBegin = from.frameBegin();
-                  srcFrameStep = frame_t(1);
-                  srcFrameEnd = from.frameEnd()+1;
-                  dstFrameBegin = to.frameEnd()+1;
-                  dstFrameStep = frame_t(1);
-                }
-                else {
-                  srcFrameBegin = from.frameEnd();
-                  srcFrameStep = frame_t(-1);
-                  srcFrameEnd = from.frameBegin()-1;
-                  dstFrameBegin = to.frameEnd()+1;
-                  dstFrameStep = frame_t(-1);
-                }
-              }
-              break;
-
-            case Copy:
-              if (place == kDocumentRangeBefore) {
-                if (to.frameBegin() <= from.frameBegin()) {
-                  srcFrameBegin = from.frameBegin();
-                  srcFrameStep = frame_t(2);
-                  srcFrameEnd = from.frameBegin() + 2*from.frames();
-                  dstFrameBegin = to.frameBegin();
-                  dstFrameStep = frame_t(1);
-                }
-                else {
-                  srcFrameBegin = from.frameEnd();
-                  srcFrameStep = frame_t(-1);
-                  srcFrameEnd = from.frameBegin()-1;
-                  dstFrameBegin = to.frameBegin();
-                  dstFrameStep = frame_t(0);
-                }
-              }
-              else if (place == kDocumentRangeAfter) {
-                if (to.frameEnd() <= from.frameBegin()) {
-                  srcFrameBegin = from.frameBegin();
-                  srcFrameStep = frame_t(2);
-                  srcFrameEnd = from.frameBegin() + 2*from.frames();
-                  dstFrameBegin = to.frameEnd()+1;
-                  dstFrameStep = frame_t(1);
-                }
-                else {
-                  srcFrameBegin = from.frameEnd();
-                  srcFrameStep = frame_t(-1);
-                  srcFrameEnd = from.frameBegin()-1;
-                  dstFrameBegin = to.frameEnd()+1;
-                  dstFrameStep = frame_t(0);
-                }
-              }
-              break;
-          }
-
-          for (frame_t srcFrame = srcFrameBegin,
-                 dstFrame = dstFrameBegin; srcFrame != srcFrameEnd; ) {
-            switch (op) {
-              case Move: api.moveFrame(sprite, srcFrame, dstFrame); break;
-              case Copy: api.copyFrame(sprite, srcFrame, dstFrame); break;
-            }
-            srcFrame += srcFrameStep;
-            dstFrame += dstFrameStep;
-          }
-
-          if (place == kDocumentRangeBefore) {
-            resultRange.startRange(LayerIndex::NoLayer, frame_t(to.frameBegin()), from.type());
-            resultRange.endRange(LayerIndex::NoLayer, frame_t(to.frameBegin()+from.frames()-1));
-          }
-          else if (place == kDocumentRangeAfter) {
-            resultRange.startRange(LayerIndex::NoLayer, frame_t(to.frameEnd()+1), from.type());
-            resultRange.endRange(LayerIndex::NoLayer, frame_t(to.frameEnd()+1+from.frames()-1));
-          }
-
-          if (op == Move && from.frameBegin() < to.frameBegin())
-            resultRange.displace(0, -from.frames());
+          move_or_copy_cels(api, op, srcLayers, dstLayers, srcFrames, dstFrames);
         }
+        else {
+          const auto& srcFrames = from.selectedFrames();
+          const auto& dstFrames = to.selectedFrames();
+
+          move_or_copy_cels(api, op, srcLayers, dstLayers, srcFrames, dstFrames);
+        }
+
+        resultRange = to;
         break;
+      }
 
-      case DocumentRange::kLayers:
-        {
-          std::vector<Layer*> layers;
-          sprite->getLayersList(layers);
+      case DocumentRange::kFrames: {
+        frame_t dstFrame;
+        if (place == kDocumentRangeBefore)
+          dstFrame = to.firstFrame();
+        else
+          dstFrame = to.lastFrame()+1;
 
-          if (layers.empty())
+        resultRange =
+          move_or_copy_frames(api, op, sprite,
+                              from.selectedFrames(), dstFrame);
+        break;
+      }
+
+      case DocumentRange::kLayers: {
+        LayerList allLayers = sprite->allBrowsableLayers();
+        if (allLayers.empty())
+          break;
+
+        LayerList srcLayers = from.selectedLayers().toLayerList();
+        LayerList dstLayers = to.selectedLayers().toLayerList();
+        ASSERT(!srcLayers.empty());
+
+        switch (op) {
+
+          case Move:
+            if (place == kDocumentRangeBefore) {
+              Layer* beforeThis = (!dstLayers.empty() ? dstLayers.front(): nullptr);
+              Layer* afterThis  = nullptr;
+
+              for (Layer* srcLayer : srcLayers) {
+                if (afterThis)
+                  api.restackLayerAfter(srcLayer, parent, afterThis);
+                else
+                  api.restackLayerBefore(srcLayer, parent, beforeThis);
+
+                afterThis = srcLayer;
+              }
+            }
+            else if (place == kDocumentRangeAfter) {
+              Layer* afterThis = (!dstLayers.empty() ? dstLayers.back(): nullptr);
+              for (Layer* srcLayer : srcLayers) {
+                api.restackLayerAfter(srcLayer, parent, afterThis);
+                afterThis = srcLayer;
+              }
+            }
+
+            // Same set of layers than the "from" range
+            resultRange = from;
             break;
 
-          switch (op) {
+          case Copy: {
+            if (place == kDocumentRangeBefore) {
+              Layer* beforeThis = (!dstLayers.empty() ? dstLayers.front(): nullptr);
+              for (Layer* srcLayer :  srcLayers) {
+                Layer* copiedLayer = api.duplicateLayerBefore(
+                  srcLayer, parent, beforeThis);
 
-            case Move:
-              if (place == kDocumentRangeBefore) {
-                for (LayerIndex i = from.layerBegin(); i <= from.layerEnd(); ++i) {
-                  api.restackLayerBefore(
-                    layers[i],
-                    layers[to.layerBegin()]);
-                }
+                resultRange.startRange(copiedLayer, -1, DocumentRange::kLayers);
+                resultRange.endRange(copiedLayer, -1);
               }
-              else if (place == kDocumentRangeAfter) {
-                for (LayerIndex i = from.layerEnd(); i >= from.layerBegin(); --i) {
-                  api.restackLayerAfter(
-                    layers[i],
-                    layers[to.layerEnd()]);
-                }
-              }
-              break;
+            }
+            else if (place == kDocumentRangeAfter) {
+              std::reverse(srcLayers.begin(), srcLayers.end());
 
-            case Copy:
-              if (place == kDocumentRangeBefore) {
-                for (LayerIndex i = from.layerBegin(); i <= from.layerEnd(); ++i) {
-                  api.duplicateLayerBefore(
-                    layers[i],
-                    layers[to.layerBegin()]);
-                }
+              Layer* afterThis = (!dstLayers.empty() ? dstLayers.back(): nullptr);
+              for (Layer* srcLayer :  srcLayers) {
+                Layer* copiedLayer = api.duplicateLayerAfter(
+                  srcLayer, parent, afterThis);
+
+                resultRange.startRange(copiedLayer, -1, DocumentRange::kLayers);
+                resultRange.endRange(copiedLayer, -1);
               }
-              else if (place == kDocumentRangeAfter) {
-                for (LayerIndex i = from.layerEnd(); i >= from.layerBegin(); --i) {
-                  api.duplicateLayerAfter(
-                    layers[i],
-                    layers[to.layerEnd()]);
-                }
-              }
-              break;
+            }
+            break;
           }
-
-          if (place == kDocumentRangeBefore) {
-            resultRange.startRange(LayerIndex(to.layerBegin()), frame_t(-1), from.type());
-            resultRange.endRange(LayerIndex(to.layerBegin()+from.layers()-1), frame_t(-1));
-          }
-          else if (place == kDocumentRangeAfter) {
-            resultRange.startRange(LayerIndex(to.layerEnd()+1), frame_t(-1), from.type());
-            resultRange.endRange(LayerIndex(to.layerEnd()+1+from.layers()-1), frame_t(-1));
-          }
-
-          if (op == Move && from.layerBegin() < to.layerBegin())
-            resultRange.displace(-from.layers(), 0);
         }
         break;
+      }
     }
 
     transaction.commit();
@@ -334,12 +411,12 @@ static DocumentRange drop_range_op(
 
 DocumentRange move_range(Document* doc, const DocumentRange& from, const DocumentRange& to, DocumentRangePlace place)
 {
-  return drop_range_op(doc, Move, from, place, to);
+  return drop_range_op(doc, Move, from, place, DocumentRange(to));
 }
 
 DocumentRange copy_range(Document* doc, const DocumentRange& from, const DocumentRange& to, DocumentRangePlace place)
 {
-  return drop_range_op(doc, Copy, from, place, to);
+  return drop_range_op(doc, Copy, from, place, DocumentRange(to));
 }
 
 void reverse_frames(Document* doc, const DocumentRange& range)
@@ -350,29 +427,28 @@ void reverse_frames(Document* doc, const DocumentRange& range)
   Transaction transaction(writer.context(), "Reverse Frames");
   DocumentApi api = doc->getApi(transaction);
   Sprite* sprite = doc->sprite();
+  LayerList layers;
   frame_t frameBegin, frameEnd;
-  int layerBegin, layerEnd;
   bool moveFrames = false;
   bool swapCels = false;
 
   switch (range.type()) {
     case DocumentRange::kCels:
-      frameBegin = range.frameBegin();
-      frameEnd = range.frameEnd();
-      layerBegin = range.layerBegin();
-      layerEnd = range.layerEnd() + 1;
+      frameBegin = range.firstFrame();
+      frameEnd = range.lastFrame();
+      layers = range.selectedLayers().toLayerList();
       swapCels = true;
       break;
     case DocumentRange::kFrames:
-      frameBegin = range.frameBegin();
-      frameEnd = range.frameEnd();
+      frameBegin = range.firstFrame();
+      frameEnd = range.lastFrame();
+      layers = sprite->allLayers();
       moveFrames = true;
       break;
     case DocumentRange::kLayers:
       frameBegin = frame_t(0);
       frameEnd = sprite->totalFrames()-1;
-      layerBegin = range.layerBegin();
-      layerEnd = range.layerEnd() + 1;
+      layers = range.selectedLayers().toLayerList();
       swapCels = true;
       break;
   }
@@ -385,10 +461,10 @@ void reverse_frames(Document* doc, const DocumentRange& range)
     }
   }
   else if (swapCels) {
-    std::vector<Layer*> layers;
-    sprite->getLayersList(layers);
+    for (Layer* layer : layers) {
+      if (!layer->isImage())
+        continue;
 
-    for (int layerIdx = layerBegin; layerIdx != layerEnd; ++layerIdx) {
       for (frame_t frame = frameBegin,
              frameRev = frameEnd;
            frame != (frameBegin+frameEnd)/2+1;
@@ -396,8 +472,8 @@ void reverse_frames(Document* doc, const DocumentRange& range)
         if (frame == frameRev)
           continue;
 
-        LayerImage* layer = static_cast<LayerImage*>(layers[layerIdx]);
-        api.swapCel(layer, frame, frameRev);
+        LayerImage* imageLayer = static_cast<LayerImage*>(layer);
+        api.swapCel(imageLayer, frame, frameRev);
       }
     }
   }
diff --git a/src/app/document_range_ops.h b/src/app/document_range_ops.h
index 6dc313f44..fb651a106 100644
--- a/src/app/document_range_ops.h
+++ b/src/app/document_range_ops.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -18,6 +18,7 @@ namespace app {
   enum DocumentRangePlace {
     kDocumentRangeBefore,
     kDocumentRangeAfter,
+    kDocumentRangeFirstChild,
   };
 
   // These functions returns the new location of the "from" range or
diff --git a/src/app/document_range_tests.cpp b/src/app/document_range_tests.cpp
index d8b5deae3..216b99b00 100644
--- a/src/app/document_range_tests.cpp
+++ b/src/app/document_range_tests.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -21,15 +21,59 @@
 using namespace app;
 using namespace doc;
 
-namespace app {
+namespace std {
 
-  std::ostream& operator<<(std::ostream& os, const DocumentRange& range) {
-    return os << "{ layers: [" << range.layerBegin() << ", " << range.layerEnd() << "]"
-              << ", frames: [" << range.frameBegin() << ", " << range.frameEnd() << "] }";
+std::ostream& operator<<(std::ostream& os, const doc::Layer* layer) {
+  if (layer)
+    os << '"' << layer->name() << '"';
+  else
+    os << "(null layer)";
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os, const app::DocumentRange& range) {
+  os << "{ layers: [";
+
+  bool first = true;
+  for (auto layer : range.selectedLayers()) {
+    if (first)
+      first = false;
+    else
+      os << ", ";
+    os << layer;
   }
 
+  os << "]";
+  os << ", frames: [";
+
+  first = true;
+  for (auto frame : range.selectedFrames()) {
+    if (first)
+      first = false;
+    else
+      os << ", ";
+    os << frame;
+  }
+
+  os << "] }";
+  return os;
 }
 
+std::ostream& operator<<(std::ostream& os, const doc::LayerList& layers) {
+  os << "[";
+  bool first = true;
+  for (auto layer : layers) {
+    if (first)
+      first = false;
+    else
+      os << ", ";
+    os << layer;
+  }
+  return os << "]";
+}
+
+} // namespace std
+
 typedef base::UniquePtr<app::Document> DocumentPtr;
 
 #define EXPECT_LAYER_ORDER(a, b, c, d) \
@@ -39,10 +83,18 @@ typedef base::UniquePtr<app::Document> DocumentPtr;
   EXPECT_TRUE(expect_layer(d, 3));
 
 #define EXPECT_FRAME_ORDER(a, b, c, d) \
-  EXPECT_TRUE(expect_frame(a, 0));     \
-  EXPECT_TRUE(expect_frame(b, 1));     \
-  EXPECT_TRUE(expect_frame(c, 2));     \
-  EXPECT_TRUE(expect_frame(d, 3));
+  EXPECT_TRUE(expect_frame(a, 0) &&    \
+              expect_frame(b, 1) &&    \
+              expect_frame(c, 2) &&    \
+              expect_frame(d, 3));
+
+#define EXPECT_FRAME_ORDER6(a, b, c, d, e, f)   \
+  EXPECT_TRUE(expect_frame(a, 0) &&             \
+              expect_frame(b, 1) &&             \
+              expect_frame(c, 2) &&             \
+              expect_frame(d, 3) &&             \
+              expect_frame(e, 4) &&             \
+              expect_frame(f, 5));
 
 #define EXPECT_FRAME_COPY1(a, b, c, d, e) \
   EXPECT_TRUE(expect_frame(a, 0));        \
@@ -77,18 +129,17 @@ typedef base::UniquePtr<app::Document> DocumentPtr;
 class DocRangeOps : public ::testing::Test {
 public:
   DocRangeOps() {
-    black = rgba(0, 0, 0, 0);
-    white = rgba(255, 255, 255, 255);
+    expected_color = rgba(255, 255, 255, 255);
 
-    doc.reset(static_cast<app::Document*>(ctx.documents().add(4, 4)));
+    doc.reset(static_cast<app::Document*>(ctx.documents().add(6, 4)));
     sprite = doc->sprite();
-    layer1 = dynamic_cast<LayerImage*>(sprite->folder()->getFirstLayer());
+    layer1 = dynamic_cast<LayerImage*>(sprite->root()->firstLayer());
     layer2 = new LayerImage(sprite);
     layer3 = new LayerImage(sprite);
     layer4 = new LayerImage(sprite);
-    sprite->folder()->addLayer(layer2);
-    sprite->folder()->addLayer(layer3);
-    sprite->folder()->addLayer(layer4);
+    sprite->root()->addLayer(layer2);
+    sprite->root()->addLayer(layer3);
+    sprite->root()->addLayer(layer4);
     EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
     layer1->setName("layer1");
@@ -96,28 +147,32 @@ public:
     layer3->setName("layer3");
     layer4->setName("layer4");
 
-    sprite->setTotalFrames(frame_t(4));
+    sprite->setTotalFrames(frame_t(6));
     sprite->setFrameDuration(frame_t(0), 1); // These durations can be used to identify
     sprite->setFrameDuration(frame_t(1), 2); // frames after a move operation
     sprite->setFrameDuration(frame_t(2), 3);
     sprite->setFrameDuration(frame_t(3), 4);
+    sprite->setFrameDuration(frame_t(4), 5);
+    sprite->setFrameDuration(frame_t(5), 6);
 
-    for (int i=0; i<4; i++) {
-      LayerImage* layer = static_cast<LayerImage*>(sprite->indexToLayer(LayerIndex(i)));
+    LayerList layers = sprite->allLayers();
 
-      for (int j=0; j<4; j++) {
+    for (layer_t i=0; i<layers.size(); i++) {
+      LayerImage* layer = static_cast<LayerImage*>(layers[i]);
+
+      for (frame_t j=0; j<sprite->totalFrames(); j++) {
         Cel* cel = layer->cel(frame_t(j));
         ImageRef image;
         if (cel)
           image = cel->imageRef();
         else {
-          image.reset(Image::create(IMAGE_RGB, 4, 4));
+          image.reset(Image::create(IMAGE_RGB, 6, 4));
           cel = new Cel(frame_t(j), image);
           layer->addCel(cel);
         }
 
-        clear_image(image.get(), black);
-        put_pixel(image.get(), i, j, white);
+        clear_image(image.get(), i + j*100);
+        put_pixel(image.get(), i, j, expected_color);
       }
     }
   }
@@ -127,19 +182,23 @@ public:
   }
 
 protected:
-  bool expect_layer(Layer* expected_layer, int layer) {
-    return expect_layer_frame(sprite->layerToIndex(expected_layer), -1, layer, -1);
+  bool expect_layer(Layer* expected_layer, layer_t layer) {
+    LayerList layers = sprite->allLayers();
+    return expect_layer_frame(
+      find_layer_index(layers, expected_layer), -1, layer, -1);
   }
 
-  bool expect_frame(int expected_frame, frame_t frame) {
-    for (int i=0; i<(int)sprite->countLayers(); ++i) {
+  bool expect_frame(layer_t expected_frame, frame_t frame) {
+    LayerList layers = sprite->allLayers();
+    for (int i=0; i<(int)layers.size(); ++i) {
       if (!expect_layer_frame(i, expected_frame, i, frame))
         return false;
     }
     return true;
   }
 
-  bool expect_layer_frame(int expected_layer, int expected_frame, int layer, frame_t frame) {
+  bool expect_layer_frame(layer_t expected_layer, frame_t expected_frame,
+                          layer_t layer, frame_t frame) {
     if (frame >= 0) {
       if (!expect_cel(expected_layer, expected_frame, layer, frame))
         return false;
@@ -149,9 +208,10 @@ protected:
     }
 
     if (layer >= 0) {
-      Layer* a = sprite->indexToLayer(LayerIndex(expected_layer));
-      Layer* b = sprite->indexToLayer(LayerIndex(layer));
-      EXPECT_EQ(a, b);
+      LayerList layers = sprite->allLayers();
+      Layer* a = layers[expected_layer];
+      Layer* b = layers[layer];
+      EXPECT_EQ(a->name(), b->name()) << layers;
       if (a != b)
         return false;
     }
@@ -159,10 +219,10 @@ protected:
     return true;
   }
 
-  bool expect_cel(int expected_layer, int expected_frame, int layer, frame_t frame) {
-    color_t expected_color = white;
-
-    Cel* cel = sprite->indexToLayer(LayerIndex(layer))->cel(frame);
+  bool expect_cel(layer_t expected_layer, frame_t expected_frame,
+                  layer_t layer, frame_t frame) {
+    LayerList layers = sprite->allLayers();
+    Cel* cel = layers[layer]->cel(frame);
     if (!cel)
       return false;
 
@@ -170,18 +230,65 @@ protected:
       cel->image(),
       expected_layer, expected_frame);
 
-    EXPECT_EQ(expected_color, color);
+    EXPECT_EQ(expected_color, color)
+      << " - expecting layer " << expected_layer << " in " << layer << " and it is " << int(color%100) << "\n"
+      << " - expecting frame " << expected_frame << " in " << frame << " and it is " << int(color/100);
 
     return (expected_color == color);
   }
 
-  bool expect_empty_cel(int layer, frame_t frame) {
-    Cel* cel = sprite->indexToLayer(LayerIndex(layer))->cel(frame);
+  bool expect_empty_cel(layer_t layer, frame_t frame) {
+    LayerList layers = sprite->allLayers();
+    Cel* cel = layers[layer]->cel(frame);
 
     EXPECT_EQ(NULL, cel);
     return (cel == NULL);
   }
 
+  DocumentRange range(Layer* fromLayer, frame_t fromFrNum, Layer* toLayer, frame_t toFrNum, DocumentRange::Type type) {
+    DocumentRange r;
+    r.startRange(fromLayer, fromFrNum, type);
+    r.endRange(toLayer, toFrNum);
+    return r;
+  }
+
+  DocumentRange range(layer_t fromLayer, frame_t fromFrNum,
+                      layer_t toLayer, frame_t toFrNum, DocumentRange::Type type) {
+    LayerList layers = sprite->allLayers();
+    return range(layers[fromLayer], fromFrNum, layers[toLayer], toFrNum, type);
+  }
+
+  DocumentRange layers_range(Layer* fromLayer, Layer* toLayer) {
+    return range(fromLayer, -1, toLayer, -1, DocumentRange::kLayers);
+  }
+
+  DocumentRange layers_range(layer_t fromLayer, layer_t toLayer) {
+    LayerList layers = sprite->allLayers();
+    return layers_range(layers[fromLayer], layers[toLayer]);
+  }
+
+  DocumentRange layers_range(Layer* layer) {
+    return range(layer, -1, layer, -1, DocumentRange::kLayers);
+  }
+
+  DocumentRange layers_range(layer_t layer) {
+    LayerList layers = sprite->allLayers();
+    return layers_range(layers[layer]);
+  }
+
+  DocumentRange frames_range(frame_t fromFrame, frame_t toFrame) {
+    return range(nullptr, fromFrame, nullptr, toFrame, DocumentRange::kFrames);
+  }
+
+  DocumentRange frames_range(frame_t frame) {
+    return range(nullptr, frame, nullptr, frame, DocumentRange::kFrames);
+  }
+
+  DocumentRange cels_range(layer_t fromLayer, frame_t fromFrNum,
+                           layer_t toLayer, frame_t toFrNum) {
+    return range(fromLayer, fromFrNum, toLayer, toFrNum, DocumentRange::kCels);
+  }
+
   TestContextT<app::Context> ctx;
   DocumentPtr doc;
   Sprite* sprite;
@@ -189,159 +296,116 @@ protected:
   LayerImage* layer2;
   LayerImage* layer3;
   LayerImage* layer4;
-  color_t black;
-  color_t white;
+  color_t expected_color;
 };
 
-inline DocumentRange range(Layer* fromLayer, frame_t fromFrNum, Layer* toLayer, frame_t toFrNum, DocumentRange::Type type) {
-  DocumentRange r;
-  r.startRange(fromLayer->sprite()->layerToIndex(fromLayer), fromFrNum, type);
-  r.endRange(toLayer->sprite()->layerToIndex(toLayer), toFrNum);
-  return r;
-}
-
-inline DocumentRange range(int fromLayer, frame_t fromFrNum, int toLayer, frame_t toFrNum, DocumentRange::Type type) {
-  DocumentRange r;
-  r.startRange(LayerIndex(fromLayer), fromFrNum, type);
-  r.endRange(LayerIndex(toLayer), toFrNum);
-  return r;
-}
-
-inline DocumentRange layers_range(Layer* fromLayer, Layer* toLayer) {
-  return range(fromLayer, -1, toLayer, -1, DocumentRange::kLayers);
-}
-
-inline DocumentRange layers_range(int fromLayer, int toLayer) {
-  return range(fromLayer, -1, toLayer, -1, DocumentRange::kLayers);
-}
-
-inline DocumentRange layers_range(Layer* layer) {
-  return range(layer, -1, layer, -1, DocumentRange::kLayers);
-}
-
-inline DocumentRange layers_range(int layer) {
-  return range(layer, -1, layer, -1, DocumentRange::kLayers);
-}
-
-inline DocumentRange frames_range(frame_t fromFrame, frame_t toFrame) {
-  return range(0, fromFrame, 0, toFrame, DocumentRange::kFrames);
-}
-
-inline DocumentRange frames_range(frame_t frame) {
-  return range(0, frame, 0, frame, DocumentRange::kFrames);
-}
-
-inline DocumentRange cels_range(int fromLayer, frame_t fromFrNum, int toLayer, frame_t toFrNum) {
-  return range(fromLayer, fromFrNum, toLayer, toFrNum, DocumentRange::kCels);
-}
-
 TEST_F(DocRangeOps, MoveLayersNoOp) {
   // Move one layer to the same place
 
   EXPECT_EQ(layers_range(layer1),
-    move_range(doc,
-      layers_range(layer1),
-      layers_range(layer1), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer1),
+                       layers_range(layer1), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer1),
-    move_range(doc,
-      layers_range(layer1),
-      layers_range(layer2), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer1),
+                       layers_range(layer2), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer4),
-    move_range(doc,
-      layers_range(layer4),
-      layers_range(layer4), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer4),
+                       layers_range(layer4), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer4),
-    move_range(doc,
-      layers_range(layer4),
-      layers_range(layer4), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer4),
+                       layers_range(layer4), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer4),
-    move_range(doc,
-      layers_range(layer4),
-      layers_range(layer3), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer4),
+                       layers_range(layer3), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   // Move two layer to the same place
 
   EXPECT_EQ(layers_range(layer1, layer2),
-    move_range(doc,
-      layers_range(layer1, layer2),
-      layers_range(layer1), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer1, layer2),
+                       layers_range(layer1), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer1, layer2),
-    move_range(doc,
-      layers_range(layer1, layer2),
-      layers_range(layer1), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer1, layer2),
+                       layers_range(layer1), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer1, layer2),
-    move_range(doc,
-      layers_range(layer1, layer2),
-      layers_range(layer2), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer1, layer2),
+                       layers_range(layer2), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer1, layer2),
-    move_range(doc,
-      layers_range(layer1, layer2),
-      layers_range(layer2), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer1, layer2),
+                       layers_range(layer2), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer1, layer2),
-    move_range(doc,
-      layers_range(layer1, layer2),
-      layers_range(layer3), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer1, layer2),
+                       layers_range(layer3), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer3, layer4),
-    move_range(doc,
-      layers_range(layer3, layer4),
-      layers_range(layer2), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer3, layer4),
+                       layers_range(layer2), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer3, layer4),
-    move_range(doc,
-      layers_range(layer3, layer4),
-      layers_range(layer3), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer3, layer4),
+                       layers_range(layer3), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer3, layer4),
-    move_range(doc,
-      layers_range(layer3, layer4),
-      layers_range(layer3), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer3, layer4),
+                       layers_range(layer3), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer3, layer4),
-    move_range(doc,
-      layers_range(layer3, layer4),
-      layers_range(layer4), kDocumentRangeBefore));
+            move_range(doc,
+                       layers_range(layer3, layer4),
+                       layers_range(layer4), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(layers_range(layer3, layer4),
-    move_range(doc,
-      layers_range(layer3, layer4),
-      layers_range(layer4), kDocumentRangeAfter));
+            move_range(doc,
+                       layers_range(layer3, layer4),
+                       layers_range(layer4), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
@@ -351,35 +415,35 @@ TEST_F(DocRangeOps, MoveLayersNoOp) {
   for (int i=0; i<2; ++i) {
     for (int layer=0; layer<4; ++layer) {
       EXPECT_EQ(layers_range(layer1, layer4),
-        move_range(doc,
-          layers_range(layer1, layer4),
-          layers_range(layer), places[i]));
+                move_range(doc,
+                           layers_range(layer1, layer4),
+                           layers_range(layer), places[i]));
       EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     for (int layer=0; layer<3; ++layer) {
       EXPECT_EQ(layers_range(layer1, layer4),
-        move_range(doc,
-          layers_range(layer1, layer4),
-          layers_range(layer, layer+1), places[i]));
+                move_range(doc,
+                           layers_range(layer1, layer4),
+                           layers_range(layer, layer+1), places[i]));
       EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     for (int layer=0; layer<2; ++layer) {
       EXPECT_EQ(layers_range(layer1, layer4),
-        move_range(doc,
-          layers_range(layer1, layer4),
-          layers_range(layer, layer+2), places[i]));
+                move_range(doc,
+                           layers_range(layer1, layer4),
+                           layers_range(layer, layer+2), places[i]));
       EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     EXPECT_EQ(layers_range(layer1, layer4),
-      move_range(doc,
-        layers_range(layer1, layer4),
-        layers_range(layer1, layer4), places[i]));
+              move_range(doc,
+                         layers_range(layer1, layer4),
+                         layers_range(layer1, layer4), places[i]));
     EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
     EXPECT_FALSE(doc->undoHistory()->canUndo());
   }
@@ -389,109 +453,109 @@ TEST_F(DocRangeOps, MoveFramesNoOp) {
   // Move one frame to the same place
 
   EXPECT_EQ(frames_range(0),
-    move_range(doc,
-      frames_range(0),
-      frames_range(0), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(0),
+                       frames_range(0), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(0),
-    move_range(doc,
-      frames_range(0),
-      frames_range(1), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(0),
+                       frames_range(1), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(3),
-    move_range(doc,
-      frames_range(3),
-      frames_range(3), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(3),
+                       frames_range(3), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(3),
-    move_range(doc,
-      frames_range(3),
-      frames_range(3), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(3),
+                       frames_range(3), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(3),
-    move_range(doc,
-      frames_range(3),
-      frames_range(2), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(3),
+                       frames_range(2), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   // Move two frame to the same place
 
   EXPECT_EQ(frames_range(0, 1),
-    move_range(doc,
-      frames_range(0, 1),
-      frames_range(0), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(0, 1),
+                       frames_range(0), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(0, 1),
-    move_range(doc,
-      frames_range(0, 1),
-      frames_range(0), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(0, 1),
+                       frames_range(0), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(0, 1),
-    move_range(doc,
-      frames_range(0, 1),
-      frames_range(1), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(0, 1),
+                       frames_range(1), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(0, 1),
-    move_range(doc,
-      frames_range(0, 1),
-      frames_range(1), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(0, 1),
+                       frames_range(1), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(0, 1),
-    move_range(doc,
-      frames_range(0, 1),
-      frames_range(2), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(0, 1),
+                       frames_range(2), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(2, 3),
-    move_range(doc,
-      frames_range(2, 3),
-      frames_range(1), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(1), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(2, 3),
-    move_range(doc,
-      frames_range(2, 3),
-      frames_range(2), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(2), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(2, 3),
-    move_range(doc,
-      frames_range(2, 3),
-      frames_range(2), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(2), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(2, 3),
-    move_range(doc,
-      frames_range(2, 3),
-      frames_range(3), kDocumentRangeBefore));
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(3), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
   EXPECT_EQ(frames_range(2, 3),
-    move_range(doc,
-      frames_range(2, 3),
-      frames_range(3), kDocumentRangeAfter));
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(3), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
   EXPECT_FALSE(doc->undoHistory()->canUndo());
 
@@ -501,42 +565,50 @@ TEST_F(DocRangeOps, MoveFramesNoOp) {
   for (int i=0; i<2; ++i) {
     for (int frame=0; frame<4; ++frame) {
       EXPECT_EQ(frames_range(0, 3),
-        move_range(doc,
-          frames_range(0, 3),
-          frames_range(frame), places[i]));
+                move_range(doc,
+                           frames_range(0, 3),
+                           frames_range(frame), places[i]));
       EXPECT_FRAME_ORDER(0, 1, 2, 3);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     for (int frame=0; frame<3; ++frame) {
       EXPECT_EQ(frames_range(0, 3),
-        move_range(doc,
-          frames_range(0, 3),
-          frames_range(frame, frame+1), places[i]));
+                move_range(doc,
+                           frames_range(0, 3),
+                           frames_range(frame, frame+1), places[i]));
       EXPECT_FRAME_ORDER(0, 1, 2, 3);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     for (int frame=0; frame<2; ++frame) {
       EXPECT_EQ(frames_range(0, 3),
-        move_range(doc,
-          frames_range(0, 3),
-          frames_range(frame, frame+2), places[i]));
+                move_range(doc,
+                           frames_range(0, 3),
+                           frames_range(frame, frame+2), places[i]));
       EXPECT_FRAME_ORDER(0, 1, 2, 3);
       EXPECT_FALSE(doc->undoHistory()->canUndo());
     }
 
     EXPECT_EQ(frames_range(0, 3),
-      move_range(doc,
-        frames_range(0, 3),
-        frames_range(0, 3), places[i]));
+              move_range(doc,
+                         frames_range(0, 3),
+                         frames_range(0, 3), places[i]));
     EXPECT_FRAME_ORDER(0, 1, 2, 3);
     EXPECT_FALSE(doc->undoHistory()->canUndo());
   }
 }
 
 TEST_F(DocRangeOps, MoveCelsNoOp) {
-  // TODO
+  EXPECT_EQ(cels_range(0, 0, 1, 1),
+            move_range(doc,
+                       cels_range(0, 0, 1, 1),
+                       cels_range(0, 0, 1, 1), kDocumentRangeAfter));
+  EXPECT_CEL(0, 0, 0, 0);
+  EXPECT_CEL(0, 1, 0, 1);
+  EXPECT_CEL(1, 0, 1, 0);
+  EXPECT_CEL(1, 1, 1, 1);
+  EXPECT_FALSE(doc->undoHistory()->canUndo());
 }
 
 TEST_F(DocRangeOps, CopyCelsNoOp) {
@@ -544,25 +616,21 @@ TEST_F(DocRangeOps, CopyCelsNoOp) {
 }
 
 TEST_F(DocRangeOps, MoveLayers) {
-  DocumentRange result;
-
   // One layer at the bottom of another
-  result = move_range(doc,
-    layers_range(layer1),
-    layers_range(layer2), kDocumentRangeAfter);
+  EXPECT_EQ(layers_range(layer1),
+            move_range(doc,
+                       layers_range(layer1),
+                       layers_range(layer2), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer2, layer1, layer3, layer4);
-  EXPECT_EQ(layers_range(layer1), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
   // One layer at the bottom
-  result = move_range(doc,
-    layers_range(layer2),
-    layers_range(layer1), kDocumentRangeBefore);
+  EXPECT_EQ(layers_range(layer2),
+            move_range(doc,
+                       layers_range(layer2),
+                       layers_range(layer1), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer2, layer1, layer3, layer4);
-  EXPECT_EQ(layers_range(layer2), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
@@ -577,46 +645,43 @@ TEST_F(DocRangeOps, MoveLayers) {
   layer1->setBackground(false);
 
   // Move one layer to the top
-  result = move_range(doc,
-    layers_range(layer2),
-    layers_range(layer4), kDocumentRangeAfter);
+  EXPECT_EQ(layers_range(layer2),
+            move_range(doc,
+                       layers_range(layer2),
+                       layers_range(layer4), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer3, layer4, layer2);
-  EXPECT_EQ(layers_range(layer2), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
   // Move one layers before other
-  result = move_range(doc,
-    layers_range(layer2),
-    layers_range(layer4), kDocumentRangeBefore);
+  EXPECT_EQ(layers_range(layer2),
+            move_range(doc,
+                       layers_range(layer2),
+                       layers_range(layer4), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer1, layer3, layer2, layer4);
-  EXPECT_EQ(layers_range(layer2), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
-  result = move_range(doc,
-    layers_range(layer1),
-    layers_range(layer3, layer4), kDocumentRangeBefore);
+  EXPECT_EQ(layers_range(layer1),
+            move_range(doc,
+                       layers_range(layer1),
+                       layers_range(layer3, layer4), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer2, layer1, layer3, layer4);
-  EXPECT_EQ(layers_range(layer1), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
   // Move two layers on top of other
-  result = move_range(doc,
-    layers_range(layer2, layer3),
-    layers_range(layer4), kDocumentRangeAfter);
+  EXPECT_EQ(layers_range(layer2, layer3),
+            move_range(doc,
+                       layers_range(layer2, layer3),
+                       layers_range(layer4), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer4, layer2, layer3);
-  EXPECT_EQ(layers_range(layer2, layer3), result);
 
-  result = move_range(doc,
-    layers_range(layer2, layer3),
-    layers_range(layer1), kDocumentRangeAfter);
+  EXPECT_EQ(layers_range(layer2, layer3),
+            move_range(doc,
+                       layers_range(layer2, layer3),
+                       layers_range(layer1), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
-  EXPECT_EQ(layers_range(layer2, layer3), result);
 
   // Move three layers at the bottom (but we cannot because the bottom is a background layer)
   layer1->setBackground(true);
@@ -629,85 +694,243 @@ TEST_F(DocRangeOps, MoveLayers) {
   layer1->setBackground(false);
 
   // Move three layers at the top
-  result = move_range(doc,
-    layers_range(layer1, layer3),
-    layers_range(layer4), kDocumentRangeAfter);
+  EXPECT_EQ(layers_range(layer1, layer3),
+            move_range(doc,
+                       layers_range(layer1, layer3),
+                       layers_range(layer4), kDocumentRangeAfter));
   EXPECT_LAYER_ORDER(layer4, layer1, layer2, layer3);
-  EXPECT_EQ(layers_range(layer1, layer3), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 
   // Move three layers at the bottom
-  result = move_range(doc,
-    layers_range(layer2, layer4),
-    layers_range(layer1), kDocumentRangeBefore);
+  EXPECT_EQ(layers_range(layer2, layer4),
+            move_range(doc,
+                       layers_range(layer2, layer4),
+                       layers_range(layer1), kDocumentRangeBefore));
   EXPECT_LAYER_ORDER(layer2, layer3, layer4, layer1);
-  EXPECT_EQ(layers_range(layer2, layer4), result);
-
   doc->undoHistory()->undo();
   EXPECT_LAYER_ORDER(layer1, layer2, layer3, layer4);
 }
 
 TEST_F(DocRangeOps, MoveFrames) {
-  move_range(doc,
-    frames_range(0, 0),
-    frames_range(1, 1), kDocumentRangeAfter);
+  // Move frame 0 after 1
+  EXPECT_EQ(frames_range(1),
+            move_range(doc,
+                       frames_range(0),
+                       frames_range(1), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(1, 0, 2, 3);
-
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  // Move one frame at the end
-  move_range(doc,
-    frames_range(1, 1),
-    frames_range(3, 3), kDocumentRangeAfter);
+  // Move frame 1 after frame 5 (at the end)
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+  EXPECT_EQ(frames_range(5),
+            move_range(doc,
+                       frames_range(1),
+                       frames_range(5), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 2, 3, 4, 5, 1);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move frames 1,2 after 5
+  EXPECT_EQ(frames_range(4, 5),
+            move_range(
+              doc,
+              frames_range(1, 2),
+              frames_range(5), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 3, 4, 5, 1, 2);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move frames 1,2 after 3
+  EXPECT_EQ(frames_range(1, 2),
+            move_range(doc,
+                       frames_range(2, 3),
+                       frames_range(0), kDocumentRangeAfter));
   EXPECT_FRAME_ORDER(0, 2, 3, 1);
-
-  doc->undoHistory()->undo();
-  EXPECT_FRAME_ORDER(0, 1, 2, 3);
-
-  // Move two frames after other
-  move_range(doc,
-    frames_range(1, 2),
-    frames_range(3, 3), kDocumentRangeAfter);
-  EXPECT_FRAME_ORDER(0, 3, 1, 2);
-
-  doc->undoHistory()->undo();
-  EXPECT_FRAME_ORDER(0, 1, 2, 3);
-
-  move_range(doc,
-    frames_range(2, 3),
-    frames_range(0, 0), kDocumentRangeAfter);
-  EXPECT_FRAME_ORDER(0, 2, 3, 1);
-
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
   // Move three frames at the beginning
-  move_range(doc,
-    frames_range(1, 3),
-    frames_range(0, 0), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(0, 2),
+            move_range(doc,
+                       frames_range(1, 3),
+                       frames_range(0), kDocumentRangeBefore));
   EXPECT_FRAME_ORDER(1, 2, 3, 0);
-
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move three frames at the end
+  EXPECT_EQ(frames_range(1, 3),
+            move_range(doc,
+                       frames_range(0, 2),
+                       frames_range(3), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER(3, 0, 1, 2);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+}
+
+TEST_F(DocRangeOps, MoveFramesNonAdjacent) {
+  // Move frames 0,2...
+
+  DocumentRange from;
+  from.startRange(nullptr, 0, DocumentRange::kFrames); from.endRange(nullptr, 0);
+  from.startRange(nullptr, 2, DocumentRange::kFrames); from.endRange(nullptr, 2);
+
+  // Move frames 0,2 after 3...
+
+  EXPECT_EQ(frames_range(2, 3),
+            move_range(doc, from, frames_range(3), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER(1, 3, 0, 2);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move frames 0,2 before 3...
+
+  EXPECT_EQ(frames_range(1, 2),
+            move_range(doc, from, frames_range(3), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER(1, 0, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move frames 0,2 before 0...
+
+  EXPECT_EQ(frames_range(0, 1),
+            move_range(doc, from, frames_range(0), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER(0, 2, 1, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move frames 0,2 after 0...
+
+  EXPECT_EQ(frames_range(0, 1),
+            move_range(doc, from, frames_range(0), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER(0, 2, 1, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move frames 0,2 before 1...
+
+  EXPECT_EQ(frames_range(0, 1),
+            move_range(doc, from, frames_range(1), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER(0, 2, 1, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move frames 0,2 after 1...
+
+  EXPECT_EQ(frames_range(1, 2),
+            move_range(doc, from, frames_range(1), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER(1, 0, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Move 1,2,5...
+
+  from.clearRange();
+  from.startRange(nullptr, 1, DocumentRange::kFrames);
+  from.endRange(nullptr, 2);
+  from.startRange(nullptr, 5, DocumentRange::kFrames);
+  from.endRange(nullptr, 5);
+
+  // Move 1,2,5 before 4...
+
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+  EXPECT_EQ(frames_range(2, 4),
+            move_range(doc, from, frames_range(4), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER6(0, 3, 1, 2, 5, 4);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,2,5 after 4...
+
+  EXPECT_EQ(frames_range(3, 5),
+            move_range(doc, from, frames_range(4), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 3, 4, 1, 2, 5);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,2,5 before 2...
+
+  EXPECT_EQ(frames_range(1, 3),
+            move_range(doc, from, frames_range(2), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER6(0, 1, 2, 5, 3, 4);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,2,5 after 2...
+
+  EXPECT_EQ(frames_range(1, 3),
+            move_range(doc, from, frames_range(2), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 1, 2, 5, 3, 4);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,2,5 before 1...
+
+  EXPECT_EQ(frames_range(1, 3),
+            move_range(doc, from, frames_range(1), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER6(0, 1, 2, 5, 3, 4);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,3,5...
+
+  from.clearRange();
+  from.startRange(nullptr, 1, DocumentRange::kFrames);
+  from.endRange(nullptr, 1);
+  from.startRange(nullptr, 3, DocumentRange::kFrames);
+  from.endRange(nullptr, 3);
+  from.startRange(nullptr, 5, DocumentRange::kFrames);
+  from.endRange(nullptr, 5);
+
+  // Move 1,3,5 before 4...
+
+  EXPECT_EQ(frames_range(2, 4),
+            move_range(doc, from, frames_range(4), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER6(0, 2, 1, 3, 5, 4);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,3,5 after 4...
+
+  EXPECT_EQ(frames_range(3, 5),
+            move_range(doc, from, frames_range(4), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 2, 4, 1, 3, 5);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,3,5 before 5...
+
+  EXPECT_EQ(frames_range(3, 5),
+            move_range(doc, from, frames_range(5), kDocumentRangeBefore));
+  EXPECT_FRAME_ORDER6(0, 2, 4, 1, 3, 5);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
+
+  // Move 1,3,5 after 5...
+
+  EXPECT_EQ(frames_range(3, 5),
+            move_range(doc, from, frames_range(5), kDocumentRangeAfter));
+  EXPECT_FRAME_ORDER6(0, 2, 4, 1, 3, 5);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER6(0, 1, 2, 3, 4, 5);
 }
 
 TEST_F(DocRangeOps, MoveCels) {
   DocumentRangePlace ignore = kDocumentRangeBefore;
 
   move_range(doc,
-    cels_range(0, 0, 0, 0),
-    cels_range(0, 1, 0, 1), ignore);
+             cels_range(0, 0, 0, 0),
+             cels_range(0, 1, 0, 1), ignore);
   EXPECT_CEL(0, 0, 0, 1);
   EXPECT_EMPTY_CEL(0, 0);
   doc->undoHistory()->undo();
   EXPECT_CEL(0, 0, 0, 0);
 
   move_range(doc,
-    cels_range(0, 0, 0, 1),
-    cels_range(0, 2, 0, 3), ignore);
+             cels_range(0, 0, 0, 1),
+             cels_range(0, 2, 0, 3), ignore);
   EXPECT_CEL(0, 0, 0, 2);
   EXPECT_CEL(0, 1, 0, 3);
   EXPECT_EMPTY_CEL(0, 0);
@@ -715,8 +938,21 @@ TEST_F(DocRangeOps, MoveCels) {
   doc->undoHistory()->undo();
 
   move_range(doc,
-    cels_range(0, 0, 0, 3),
-    cels_range(1, 0, 1, 3), ignore);
+             cels_range(0, 0, 1, 1),
+             cels_range(2, 2, 3, 3), ignore);
+  EXPECT_CEL(0, 0, 2, 2);
+  EXPECT_CEL(0, 1, 2, 3);
+  EXPECT_CEL(1, 0, 3, 2);
+  EXPECT_CEL(1, 1, 3, 3);
+  EXPECT_EMPTY_CEL(0, 0);
+  EXPECT_EMPTY_CEL(0, 1);
+  EXPECT_EMPTY_CEL(1, 0);
+  EXPECT_EMPTY_CEL(1, 1);
+  doc->undoHistory()->undo();
+
+  move_range(doc,
+             cels_range(0, 0, 0, 3),
+             cels_range(1, 0, 1, 3), ignore);
   EXPECT_CEL(0, 0, 1, 0);
   EXPECT_CEL(0, 1, 1, 1);
   EXPECT_CEL(0, 2, 1, 2);
@@ -726,6 +962,16 @@ TEST_F(DocRangeOps, MoveCels) {
   EXPECT_EMPTY_CEL(0, 2);
   EXPECT_EMPTY_CEL(0, 3);
   doc->undoHistory()->undo();
+
+  // Moving with overlapping areas
+  move_range(doc,
+             cels_range(0, 0, 0, 2),
+             cels_range(0, 1, 0, 3), ignore);
+  EXPECT_CEL(0, 0, 0, 1);
+  EXPECT_CEL(0, 1, 0, 2);
+  EXPECT_CEL(0, 2, 0, 3);
+  EXPECT_EMPTY_CEL(0, 0);
+  doc->undoHistory()->undo();
 }
 
 TEST_F(DocRangeOps, CopyLayers) {
@@ -734,79 +980,139 @@ TEST_F(DocRangeOps, CopyLayers) {
 
 TEST_F(DocRangeOps, CopyFrames) {
   // Copy one frame
-  copy_range(doc,
-    frames_range(0),
-    frames_range(2, 3), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(2),
+            copy_range(doc,
+                       frames_range(0),
+                       frames_range(2, 3), kDocumentRangeBefore));
   EXPECT_FRAME_COPY1(0, 1, 0, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(0),
-    frames_range(2, 3), kDocumentRangeAfter);
+  EXPECT_EQ(frames_range(4),
+            copy_range(doc,
+                       frames_range(0),
+                       frames_range(2, 3), kDocumentRangeAfter));
   EXPECT_FRAME_COPY1(0, 1, 2, 3, 0);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(3),
-    frames_range(0, 1), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(0),
+            copy_range(doc,
+                       frames_range(3),
+                       frames_range(0, 1), kDocumentRangeBefore));
   EXPECT_FRAME_COPY1(3, 0, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(3),
-    frames_range(0, 1), kDocumentRangeAfter);
+  EXPECT_EQ(frames_range(2),
+            copy_range(doc,
+                       frames_range(3),
+                       frames_range(0, 1), kDocumentRangeAfter));
   EXPECT_FRAME_COPY1(0, 1, 3, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
   // Copy three frames
 
-  copy_range(doc,
-    frames_range(0, 2),
-    frames_range(3), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(3, 5),
+            copy_range(doc,
+                       frames_range(0, 2),
+                       frames_range(3), kDocumentRangeBefore));
   EXPECT_FRAME_COPY3(0, 1, 2, 0, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(0, 2),
-    frames_range(3), kDocumentRangeAfter);
+  EXPECT_EQ(frames_range(4, 6),
+            copy_range(doc,
+                       frames_range(0, 2),
+                       frames_range(3), kDocumentRangeAfter));
   EXPECT_FRAME_COPY3(0, 1, 2, 3, 0, 1, 2);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(1, 3),
-    frames_range(0), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(0, 2),
+            copy_range(doc,
+                       frames_range(1, 3),
+                       frames_range(0), kDocumentRangeBefore));
   EXPECT_FRAME_COPY3(1, 2, 3, 0, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(1, 3),
-    frames_range(0), kDocumentRangeAfter);
+  EXPECT_EQ(frames_range(1, 3),
+            copy_range(doc,
+                       frames_range(1, 3),
+                       frames_range(0), kDocumentRangeAfter));
   EXPECT_FRAME_COPY3(0, 1, 2, 3, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(0, 2),
-    frames_range(0, 2), kDocumentRangeBefore);
+  EXPECT_EQ(frames_range(0, 2),
+            copy_range(doc,
+                       frames_range(0, 2),
+                       frames_range(0, 2), kDocumentRangeBefore));
   EXPECT_FRAME_COPY3(0, 1, 2, 0, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 
-  copy_range(doc,
-    frames_range(0, 2),
-    frames_range(0, 2), kDocumentRangeAfter);
+  EXPECT_EQ(frames_range(3, 5),
+            copy_range(doc,
+                       frames_range(0, 2),
+                       frames_range(0, 2), kDocumentRangeAfter));
   EXPECT_FRAME_COPY3(0, 1, 2, 0, 1, 2, 3);
   doc->undoHistory()->undo();
   EXPECT_FRAME_ORDER(0, 1, 2, 3);
 }
 
+TEST_F(DocRangeOps, CopyFramesNonAdjacent) {
+  // Copy frames 0 and 2...
+
+  DocumentRange from;
+  from.startRange(nullptr, 0, DocumentRange::kFrames); from.endRange(nullptr, 0);
+  from.startRange(nullptr, 2, DocumentRange::kFrames); from.endRange(nullptr, 2);
+
+  EXPECT_EQ(frames_range(3, 4),
+            copy_range(doc, from, frames_range(3), kDocumentRangeBefore));
+  EXPECT_FRAME_COPY2(0, 1, 2, 0, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  EXPECT_EQ(frames_range(4, 5),
+            copy_range(doc, from, frames_range(3), kDocumentRangeAfter));
+  EXPECT_FRAME_COPY2(0, 1, 2, 3, 0, 2);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  EXPECT_EQ(frames_range(2, 3),
+            copy_range(doc, from, frames_range(1), kDocumentRangeAfter));
+  EXPECT_FRAME_COPY2(0, 1, 0, 2, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  EXPECT_EQ(frames_range(1, 2),
+            copy_range(doc, from, frames_range(1), kDocumentRangeBefore));
+  EXPECT_FRAME_COPY2(0, 0, 2, 1, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  // Copy frames 1 and 3...
+
+  from.clearRange();
+  from.startRange(nullptr, 1, DocumentRange::kFrames); from.endRange(nullptr, 1);
+  from.startRange(nullptr, 3, DocumentRange::kFrames); from.endRange(nullptr, 3);
+
+  EXPECT_EQ(frames_range(0, 1),
+            copy_range(doc, from, frames_range(0), kDocumentRangeBefore));
+  EXPECT_FRAME_COPY2(1, 3, 0, 1, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+
+  EXPECT_EQ(frames_range(1, 2),
+            copy_range(doc, from, frames_range(0), kDocumentRangeAfter));
+  EXPECT_FRAME_COPY2(0, 1, 3, 1, 2, 3);
+  doc->undoHistory()->undo();
+  EXPECT_FRAME_ORDER(0, 1, 2, 3);
+}
+
 TEST_F(DocRangeOps, CopyCels) {
   // TODO
 }
diff --git a/src/app/file/ase_format.cpp b/src/app/file/ase_format.cpp
index fbf007bea..b611a2b1c 100644
--- a/src/app/file/ase_format.cpp
+++ b/src/app/file/ase_format.cpp
@@ -100,11 +100,12 @@ static void ase_file_read_frame_header(FILE* f, ASE_FrameHeader* frame_header);
 static void ase_file_prepare_frame_header(FILE* f, ASE_FrameHeader* frame_header);
 static void ase_file_write_frame_header(FILE* f, ASE_FrameHeader* frame_header);
 
-static void ase_file_write_layers(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer);
-static void ase_file_write_cels(FILE* f, ASE_FrameHeader* frame_header,
-                                const Sprite* sprite, const Layer* layer,
-                                const frame_t frame,
-                                const frame_t firstFrame);
+static void ase_file_write_layers(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer, int child_level);
+static layer_t ase_file_write_cels(FILE* f, ASE_FrameHeader* frame_header,
+                                   const Sprite* sprite, const Layer* layer,
+                                   layer_t layer_index,
+                                   const frame_t frame,
+                                   const frame_t firstFrame);
 
 static void ase_file_read_padding(FILE* f, int bytes);
 static void ase_file_write_padding(FILE* f, int bytes);
@@ -120,10 +121,12 @@ static Palette* ase_file_read_palette_chunk(FILE* f, Palette* prevPal, frame_t f
 static void ase_file_write_color2_chunk(FILE* f, ASE_FrameHeader* frame_header, const Palette* pal);
 static void ase_file_write_palette_chunk(FILE* f, ASE_FrameHeader* frame_header, const Palette* pal, int from, int to);
 static Layer* ase_file_read_layer_chunk(FILE* f, ASE_Header* header, Sprite* sprite, Layer** previous_layer, int* current_level);
-static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer);
-static Cel* ase_file_read_cel_chunk(FILE* f, Sprite* sprite, frame_t frame, PixelFormat pixelFormat, FileOp* fop, ASE_Header* header, size_t chunk_end);
+static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer, int child_level);
+static Cel* ase_file_read_cel_chunk(FILE* f, Sprite* sprite, LayerList& allLayers, frame_t frame, PixelFormat pixelFormat, FileOp* fop, ASE_Header* header, size_t chunk_end);
 static void ase_file_write_cel_chunk(FILE* f, ASE_FrameHeader* frame_header,
-                                     const Cel* cel, const LayerImage* layer,
+                                     const Cel* cel,
+                                     const LayerImage* layer,
+                                     const layer_t layer_index,
                                      const Sprite* sprite,
                                      const frame_t firstFrame);
 static Mask* ase_file_read_mask_chunk(FILE* f);
@@ -135,8 +138,8 @@ static void ase_file_write_frame_tags_chunk(FILE* f, ASE_FrameHeader* frame_head
                                             const frame_t fromFrame, const frame_t toFrame);
 static void ase_file_read_user_data_chunk(FILE* f, UserData* userData);
 static void ase_file_write_user_data_chunk(FILE* f, ASE_FrameHeader* frame_header, const UserData* userData);
-static bool ase_has_groups(LayerFolder* layer);
-static void ase_ungroup_all(LayerFolder* layer);
+static bool ase_has_groups(LayerGroup* group);
+static void ase_ungroup_all(LayerGroup* group);
 
 class ChunkWriter {
 public:
@@ -213,9 +216,10 @@ bool AseFormat::onLoad(FileOp* fop)
   sprite->setPixelRatio(PixelRatio(header.pixel_width, header.pixel_height));
 
   // Prepare variables for layer chunks
-  Layer* last_layer = sprite->folder();
+  Layer* last_layer = sprite->root();
   WithUserData* last_object_with_user_data = nullptr;
   int current_level = -1;
+  LayerList allLayers;
 
   // Read frame by frame to end-of-file
   for (frame_t frame(0); frame<sprite->totalFrames(); ++frame) {
@@ -235,7 +239,7 @@ bool AseFormat::onLoad(FileOp* fop)
 
       // Read chunks
       for (int c=0; c<frame_header.chunks; c++) {
-        /* start chunk position */
+        // Start chunk position
         int chunk_pos = ftell(f);
         fop->setProgress((float)chunk_pos / (float)header.size);
 
@@ -270,16 +274,20 @@ bool AseFormat::onLoad(FileOp* fop)
           }
 
           case ASE_FILE_CHUNK_LAYER: {
-            last_object_with_user_data =
+            Layer* newLayer =
               ase_file_read_layer_chunk(f, &header, sprite,
                                         &last_layer,
                                         &current_level);
+            if (newLayer) {
+              allLayers.push_back(newLayer);
+              last_object_with_user_data = newLayer;
+            }
             break;
           }
 
           case ASE_FILE_CHUNK_CEL: {
             Cel* cel =
-              ase_file_read_cel_chunk(f, sprite, frame,
+              ase_file_read_cel_chunk(f, sprite, allLayers, frame,
                                       sprite->pixelFormat(), fop, &header,
                                       chunk_pos+chunk_size);
             if (cel) {
@@ -348,7 +356,7 @@ bool AseFormat::onLoad(FileOp* fop)
 
 bool AseFormat::onPostLoad(FileOp* fop)
 {
-  LayerFolder* folder = fop->document()->sprite()->folder();
+  LayerGroup* group = fop->document()->sprite()->root();
 
   // Forward Compatibility: In 1.1 we convert a file with layer groups
   // (saved with 1.2) as top level layers
@@ -356,7 +364,7 @@ bool AseFormat::onPostLoad(FileOp* fop)
   bool flat = (ver[0] == '1' &&
                ver[1] == '.' &&
                ver[2] == '1');
-  if (flat && ase_has_groups(folder)) {
+  if (flat && ase_has_groups(group)) {
     if (fop->context() &&
         fop->context()->isUIAvailable() &&
         ui::Alert::show("Warning"
@@ -369,7 +377,7 @@ bool AseFormat::onPostLoad(FileOp* fop)
                         PACKAGE, ver.c_str()) != 1) {
       return false;
     }
-    ase_ungroup_all(folder);
+    ase_ungroup_all(group);
   }
   return true;
 }
@@ -426,12 +434,9 @@ bool AseFormat::onSave(FileOp* fop)
 
     // Write extra chunks in the first frame
     if (frame == fop->roi().fromFrame()) {
-      LayerIterator it = sprite->folder()->getLayerBegin();
-      LayerIterator end = sprite->folder()->getLayerEnd();
-
       // Write layer chunks
-      for (; it != end; ++it)
-        ase_file_write_layers(f, &frame_header, *it);
+      for (Layer* child : sprite->root()->layers())
+        ase_file_write_layers(f, &frame_header, child, 0);
 
       // Writer frame tags
       if (sprite->frameTags().size() > 0)
@@ -442,8 +447,8 @@ bool AseFormat::onSave(FileOp* fop)
 
     // Write cel chunks
     ase_file_write_cels(f, &frame_header,
-                        sprite, sprite->folder(),
-                        frame, fop->roi().fromFrame());
+                        sprite, sprite->root(),
+                        0, frame, fop->roi().fromFrame());
 
     // Write the frame header
     ase_file_write_frame_header(f, &frame_header);
@@ -608,35 +613,30 @@ static void ase_file_write_frame_header(FILE* f, ASE_FrameHeader* frame_header)
   fseek(f, end, SEEK_SET);
 }
 
-static void ase_file_write_layers(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer)
+static void ase_file_write_layers(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer, int child_index)
 {
-  ase_file_write_layer_chunk(f, frame_header, layer);
+  ase_file_write_layer_chunk(f, frame_header, layer, child_index);
   if (!layer->userData().isEmpty())
     ase_file_write_user_data_chunk(f, frame_header, &layer->userData());
 
-  if (layer->isFolder()) {
-    auto it = static_cast<const LayerFolder*>(layer)->getLayerBegin(),
-         end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
-    for (; it != end; ++it)
-      ase_file_write_layers(f, frame_header, *it);
+  if (layer->isGroup()) {
+    for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers())
+      ase_file_write_layers(f, frame_header, child, child_index+1);
   }
 }
 
-static void ase_file_write_cels(FILE* f, ASE_FrameHeader* frame_header,
-                                const Sprite* sprite, const Layer* layer,
-                                const frame_t frame,
-                                const frame_t firstFrame)
+static layer_t ase_file_write_cels(FILE* f, ASE_FrameHeader* frame_header,
+                                   const Sprite* sprite, const Layer* layer,
+                                   layer_t layer_index,
+                                   const frame_t frame,
+                                   const frame_t firstFrame)
 {
   if (layer->isImage()) {
     const Cel* cel = layer->cel(frame);
     if (cel) {
-/*       fop->setError("New cel in frame %d, in layer %d\n", */
-/*                   frame, sprite_layer2index(sprite, layer)); */
-
       ase_file_write_cel_chunk(f, frame_header, cel,
                                static_cast<const LayerImage*>(layer),
-                               sprite, firstFrame);
+                               layer_index, sprite, firstFrame);
 
       if (!cel->link() &&
           !cel->data()->userData().isEmpty()) {
@@ -646,13 +646,18 @@ static void ase_file_write_cels(FILE* f, ASE_FrameHeader* frame_header,
     }
   }
 
-  if (layer->isFolder()) {
-    auto it = static_cast<const LayerFolder*>(layer)->getLayerBegin(),
-         end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
+  if (layer != sprite->root())
+    ++layer_index;
 
-    for (; it != end; ++it)
-      ase_file_write_cels(f, frame_header, sprite, *it, frame, firstFrame);
+  if (layer->isGroup()) {
+    for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers()) {
+      layer_index =
+        ase_file_write_cels(f, frame_header, sprite, child,
+                            layer_index, frame, firstFrame);
+    }
   }
+
+  return layer_index;
 }
 
 static void ase_file_read_padding(FILE* f, int bytes)
@@ -835,25 +840,19 @@ static void ase_file_write_palette_chunk(FILE* f, ASE_FrameHeader* frame_header,
 
 static Layer* ase_file_read_layer_chunk(FILE* f, ASE_Header* header, Sprite* sprite, Layer** previous_layer, int* current_level)
 {
-  std::string name;
-  Layer* layer = NULL;
-  /* read chunk data */
-  int flags;
-  int layer_type;
-  int child_level;
-
-  flags = fgetw(f);
-  layer_type = fgetw(f);
-  child_level = fgetw(f);
+  // Read chunk data
+  int flags = fgetw(f);
+  int layer_type = fgetw(f);
+  int child_level = fgetw(f);
   fgetw(f);                     // default width
   fgetw(f);                     // default height
   int blendmode = fgetw(f);     // blend mode
   int opacity = fgetc(f);       // opacity
-
   ase_file_read_padding(f, 3);
-  name = ase_file_read_string(f);
+  std::string name = ase_file_read_string(f);
 
   // Image layer
+  Layer* layer;
   if (layer_type == 0) {
     layer = new LayerImage(sprite);
 
@@ -866,7 +865,10 @@ static Layer* ase_file_read_layer_chunk(FILE* f, ASE_Header* header, Sprite* spr
   }
   // Layer set
   else if (layer_type == 1) {
-    layer = new LayerFolder(sprite);
+    layer = new LayerGroup(sprite);
+  }
+  else {
+    layer = nullptr;
   }
 
   if (layer) {
@@ -880,7 +882,7 @@ static Layer* ase_file_read_layer_chunk(FILE* f, ASE_Header* header, Sprite* spr
     if (child_level == *current_level)
       (*previous_layer)->parent()->addLayer(layer);
     else if (child_level > *current_level)
-      static_cast<LayerFolder*>(*previous_layer)->addLayer(layer);
+      static_cast<LayerGroup*>(*previous_layer)->addLayer(layer);
     else if (child_level < *current_level)
       (*previous_layer)->parent()->parent()->addLayer(layer);
 
@@ -891,7 +893,7 @@ static Layer* ase_file_read_layer_chunk(FILE* f, ASE_Header* header, Sprite* spr
   return layer;
 }
 
-static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer)
+static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, const Layer* layer, int child_level)
 {
   ChunkWriter chunk(f, frame_header, ASE_FILE_CHUNK_LAYER);
 
@@ -899,15 +901,9 @@ static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, c
   fputw(static_cast<int>(layer->flags()), f);
 
   // Layer type
-  fputw(layer->isImage() ? 0: (layer->isFolder() ? 1: -1), f);
+  fputw(layer->isImage() ? 0: (layer->isGroup() ? 1: -1), f);
 
   // Layer child level
-  LayerFolder* parent = layer->parent();
-  int child_level = -1;
-  while (parent != NULL) {
-    child_level++;
-    parent = parent->parent();
-  }
   fputw(child_level, f);
 
   // Default width & height, and blend mode
@@ -916,13 +912,11 @@ static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, c
   fputw(layer->isImage() ? (int)static_cast<const LayerImage*>(layer)->blendMode(): 0, f);
   fputc(layer->isImage() ? (int)static_cast<const LayerImage*>(layer)->opacity(): 0, f);
 
-  // padding
+  // Padding
   ase_file_write_padding(f, 3);
 
-  /* layer name */
+  // Layer name
   ase_file_write_string(f, layer->name());
-
-  /* fop->setError("Layer name \"%s\" child level: %d\n", layer->name, child_level); */
 }
 
 //////////////////////////////////////////////////////////////////////
@@ -1189,21 +1183,25 @@ static void write_compressed_image(FILE* f, const Image* image)
 // Cel Chunk
 //////////////////////////////////////////////////////////////////////
 
-static Cel* ase_file_read_cel_chunk(FILE* f, Sprite* sprite, frame_t frame,
+static Cel* ase_file_read_cel_chunk(FILE* f,
+                                    Sprite* sprite,
+                                    LayerList& allLayers,
+                                    frame_t frame,
                                     PixelFormat pixelFormat,
                                     FileOp* fop, ASE_Header* header, size_t chunk_end)
 {
-  /* read chunk data */
-  LayerIndex layer_index = LayerIndex(fgetw(f));
+  // Read chunk data
+  layer_t layer_index = fgetw(f);
   int x = ((short)fgetw(f));
   int y = ((short)fgetw(f));
   int opacity = fgetc(f);
   int cel_type = fgetw(f);
-  Layer* layer;
-
   ase_file_read_padding(f, 7);
 
-  layer = sprite->indexToLayer(layer_index);
+  Layer* layer = nullptr;
+  if (layer_index >= 0 && layer_index < layer_t(allLayers.size()))
+    layer = allLayers[layer_index];
+
   if (!layer) {
     fop->setError("Frame %d didn't found layer with index %d\n",
                   (int)frame, (int)layer_index);
@@ -1326,13 +1324,14 @@ static Cel* ase_file_read_cel_chunk(FILE* f, Sprite* sprite, frame_t frame,
 }
 
 static void ase_file_write_cel_chunk(FILE* f, ASE_FrameHeader* frame_header,
-                                     const Cel* cel, const LayerImage* layer,
+                                     const Cel* cel,
+                                     const LayerImage* layer,
+                                     const layer_t layer_index,
                                      const Sprite* sprite,
                                      const frame_t firstFrame)
 {
   ChunkWriter chunk(f, frame_header, ASE_FILE_CHUNK_CEL);
 
-  int layer_index = sprite->layerToIndex(layer);
   const Cel* link = cel->link();
 
   // In case the original link is outside the ROI, we've to find the
@@ -1604,26 +1603,26 @@ static void ase_file_write_user_data_chunk(FILE* f, ASE_FrameHeader* frame_heade
   }
 }
 
-static bool ase_has_groups(LayerFolder* folder)
+static bool ase_has_groups(LayerGroup* group)
 {
-  for (Layer* child : folder->getLayersList()) {
-    if (child->isFolder())
+  for (Layer* child : group->layers()) {
+    if (child->isGroup())
       return true;
   }
   return false;
 }
 
-static void ase_ungroup_all(LayerFolder* folder)
+static void ase_ungroup_all(LayerGroup* group)
 {
-  LayerFolder* root = folder->sprite()->folder();
-  LayerList list = folder->getLayersList();
+  LayerGroup* root = group->sprite()->root();
+  LayerList list = group->layers();
 
   for (Layer* child : list) {
-    if (child->isFolder()) {
-      ase_ungroup_all(static_cast<LayerFolder*>(child));
-      folder->removeLayer(child);
+    if (child->isGroup()) {
+      ase_ungroup_all(static_cast<LayerGroup*>(child));
+      group->removeLayer(child);
     }
-    else if (folder != root) {
+    else if (group != root) {
       // Create a new name adding all group layer names
       {
         std::string name;
@@ -1635,14 +1634,14 @@ static void ase_ungroup_all(LayerFolder* folder)
         child->setName(name);
       }
 
-      folder->removeLayer(child);
+      group->removeLayer(child);
       root->addLayer(child);
     }
   }
 
-  if (folder != root) {
-    ASSERT(folder->getLayersCount() == 0);
-    delete folder;
+  if (group != root) {
+    ASSERT(group->layersCount() == 0);
+    delete group;
   }
 }
 
diff --git a/src/app/file/file.cpp b/src/app/file/file.cpp
index e9bb57012..3a72adb89 100644
--- a/src/app/file/file.cpp
+++ b/src/app/file/file.cpp
@@ -354,7 +354,7 @@ FileOp* FileOp::createSaveDocumentOperation(const Context* context,
   }
 
   // Layers support
-  if (fop->m_document->sprite()->folder()->getLayersCount() > 1) {
+  if (fop->m_document->sprite()->root()->layersCount() > 1) {
     if (!(fop->m_format->support(FILE_SUPPORT_LAYERS))) {
       warnings += "<<- Layers";
     }
@@ -843,7 +843,7 @@ Image* FileOp::sequenceImage(PixelFormat pixelFormat, int w, int h)
       LayerImage* layer = new LayerImage(sprite);
 
       // Add the layer
-      sprite->folder()->addLayer(layer);
+      sprite->root()->addLayer(layer);
 
       // Done
       createDocument(sprite);
diff --git a/src/app/file/file_tests.cpp b/src/app/file/file_tests.cpp
index 05515b589..27b3d403f 100644
--- a/src/app/file/file_tests.cpp
+++ b/src/app/file/file_tests.cpp
@@ -37,7 +37,7 @@ TEST(File, SeveralSizes)
         doc->setFilename(&fn[0]);
 
         // Random pixels
-        Layer* layer = doc->sprite()->folder()->getFirstLayer();
+        Layer* layer = doc->sprite()->root()->firstLayer();
         ASSERT_TRUE(layer != NULL);
         Image* image = layer->cel(frame_t(0))->image();
         std::srand(w*h);
@@ -60,7 +60,7 @@ TEST(File, SeveralSizes)
         ASSERT_EQ(h, doc->sprite()->height());
 
         // Same random pixels (see the seed)
-        Layer* layer = doc->sprite()->folder()->getFirstLayer();
+        Layer* layer = doc->sprite()->root()->firstLayer();
         ASSERT_TRUE(layer != nullptr);
         Image* image = layer->cel(frame_t(0))->image();
         std::srand(w*h);
diff --git a/src/app/file/fli_format.cpp b/src/app/file/fli_format.cpp
index 456bc59c7..1c12ea377 100644
--- a/src/app/file/fli_format.cpp
+++ b/src/app/file/fli_format.cpp
@@ -74,7 +74,7 @@ bool FliFormat::onLoad(FileOp* fop)
   // Create the sprite
   Sprite* sprite = new Sprite(IMAGE_INDEXED, w, h, 256);
   LayerImage* layer = new LayerImage(sprite);
-  sprite->folder()->addLayer(layer);
+  sprite->root()->addLayer(layer);
   layer->configureAsBackground();
 
   // Set frames and speed
diff --git a/src/app/file/gif_format.cpp b/src/app/file/gif_format.cpp
index 023d98ce5..99e1ef506 100644
--- a/src/app/file/gif_format.cpp
+++ b/src/app/file/gif_format.cpp
@@ -679,7 +679,7 @@ private:
     clear_image(m_previousImage.get(), m_bgIndex);
 
     m_layer = new LayerImage(m_sprite.get());
-    m_sprite->folder()->addLayer(m_layer);
+    m_sprite->root()->addLayer(m_layer);
   }
 
   void resetRemap(int ncolors) {
@@ -838,9 +838,7 @@ public:
         m_sprite->getPalettes().size() == 1) {
       // If some layer has opacity < 255 or a different blend mode, we
       // need to create color palettes.
-      std::vector<Layer*> layers;
-      m_sprite->getLayersList(layers);
-      for (const Layer* layer : layers) {
+      for (const Layer* layer : m_sprite->allVisibleLayers()) {
         if (layer->isVisible() && layer->isImage()) {
           const LayerImage* imageLayer = static_cast<const LayerImage*>(layer);
           if (imageLayer->opacity() < 255 ||
diff --git a/src/app/file/ico_format.cpp b/src/app/file/ico_format.cpp
index 6436dc886..1f797ae0f 100644
--- a/src/app/file/ico_format.cpp
+++ b/src/app/file/ico_format.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -127,7 +127,7 @@ bool IcoFormat::onLoad(FileOp* fop)
   // Create the sprite with one background layer
   Sprite* sprite = new Sprite(pixelFormat, width, height, numcolors);
   LayerImage* layer = new LayerImage(sprite);
-  sprite->folder()->addLayer(layer);
+  sprite->root()->addLayer(layer);
 
   // Create the first image/cel
   ImageRef image(Image::create(pixelFormat, width, height));
diff --git a/src/app/file/palette_file.cpp b/src/app/file/palette_file.cpp
index 6ebe2c0b0..cc6177a1c 100644
--- a/src/app/file/palette_file.cpp
+++ b/src/app/file/palette_file.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -119,7 +119,7 @@ bool save_palette(const char *filename, const Palette* pal, int columns)
       Sprite* sprite = doc->sprite();
       doc->sprite()->setPalette(pal, false);
 
-      Layer* layer = sprite->folder()->getFirstLayer();
+      Layer* layer = sprite->root()->firstLayer();
       Image* image = layer->cel(frame_t(0))->image();
 
       int x, y, c;
diff --git a/src/app/file/pixly_format.cpp b/src/app/file/pixly_format.cpp
index a38c03a88..226c7ce19 100644
--- a/src/app/file/pixly_format.cpp
+++ b/src/app/file/pixly_format.cpp
@@ -15,8 +15,8 @@
 #include "app/file/file.h"
 #include "app/file/file_format.h"
 #include "app/xml_document.h"
-#include "base/file_handle.h"
 #include "base/convert_to.h"
+#include "base/file_handle.h"
 #include "base/path.h"
 #include "doc/doc.h"
 #include "doc/algorithm/shrink_bounds.h"
@@ -85,7 +85,6 @@ template<typename Number> static Number check_number(const char* c_str) {
   }
 }
 
-
 bool PixlyFormat::onLoad(FileOp* fop)
 {
   try {
@@ -120,7 +119,7 @@ bool PixlyFormat::onLoad(FileOp* fop)
     sprite->setDurationForAllFrames(200);
 
     for (int i=0; i<layerCount; i++) {
-      sprite->folder()->addLayer(new LayerImage(sprite));
+      sprite->root()->addLayer(new LayerImage(sprite));
     }
 
     // load image sheet
@@ -131,16 +130,15 @@ bool PixlyFormat::onLoad(FileOp* fop)
       throw Exception("Pixly loader requires a valid PNG file");
     }
 
-    Image* sheet = sheet_doc->sprite()->layer(0)->cel(0)->image();
-
-    if (sheet->pixelFormat() != IMAGE_RGB) {
+    Image* sheet = sheet_doc->sprite()->root()->firstLayer()->cel(0)->image();
+    if (sheet->pixelFormat() != IMAGE_RGB)
       throw Exception("Pixly loader requires a RGBA PNG");
-    }
 
     int sheetWidth = sheet->width();
     int sheetHeight = sheet->height();
 
     // slice cels from sheet
+    LayerList layers = sprite->allLayers();
     std::vector<int> visible(layerCount, 0);
 
     TiXmlElement* xmlFrame = check(xmlFrames->FirstChild("Frame"))->ToElement();
@@ -150,8 +148,8 @@ bool PixlyFormat::onLoad(FileOp* fop)
 
       int index = check_number<int>(xmlIndex->Attribute("linear"));
       frame_t frame(index / layerCount);
-      LayerIndex layer_index(index % layerCount);
-      Layer *layer = sprite->indexToLayer(layer_index);
+      layer_t layer_index(index % layerCount);
+      Layer* layer = layers[layer_index];
 
       const char * duration = xmlFrame->Attribute("duration");
       if (duration) {
@@ -215,16 +213,14 @@ bool PixlyFormat::onLoad(FileOp* fop)
       fop->setProgress(0.5 + 0.5 * ((float)(index+1) / (float)imageCount));
     }
 
-    for (int i=0; i<layerCount; i++) {
-      LayerIndex layer_index(i);
-      Layer *layer = sprite->indexToLayer(layer_index);
-      layer->setVisible(visible[i] > frameCount/2);
+    for (layer_t i=0; i<layerCount; i++) {
+      layers[i]->setVisible(visible[i] > frameCount/2);
     }
 
     fop->createDocument(sprite);
     sprite.release();
   }
-  catch(Exception &e) {
+  catch(Exception& e) {
     fop->setError((std::string("Pixly file format: ")+std::string(e.what())+"\n").c_str());
     return false;
   }
@@ -237,19 +233,16 @@ bool PixlyFormat::onSave(FileOp* fop)
 {
   const Sprite* sprite = fop->document()->sprite();
 
-  auto it = sprite->folder()->getLayerBegin(),
-       end = sprite->folder()->getLayerEnd();
-  for (; it != end; ++it) { // layers
-    Layer *layer = *it;
+  for (const Layer* layer : sprite->root()->layers()) {
     if (!layer->isImage()) {
-      fop->setError("Pixly .anim file format does not support layer folders\n");
+      fop->setError("Pixly .anim file format does not support layer groups\n");
       return false;
     }
   }
 
   // account sheet size
   int frameCount = sprite->totalFrames();
-  int layerCount = sprite->folder()->getLayersCount();
+  int layerCount = sprite->root()->layersCount();
   int imageCount = frameCount * layerCount;
 
   int frameWidth = sprite->width();
@@ -263,7 +256,7 @@ bool PixlyFormat::onSave(FileOp* fop)
   // create PNG document
   Sprite* sheet_sprite = new Sprite(IMAGE_RGB, sheetWidth, sheetHeight, 256);
   LayerImage* sheet_layer = new LayerImage(sheet_sprite);
-  sheet_sprite->folder()->addLayer(sheet_layer);
+  sheet_sprite->root()->addLayer(sheet_layer);
   UniquePtr<Document> sheet_doc(new Document(sheet_sprite));
   ImageRef sheet_image(Image::create(IMAGE_RGB, sheetWidth, sheetHeight));
   Image* sheet = sheet_image.get();
@@ -291,11 +284,7 @@ bool PixlyFormat::onSave(FileOp* fop)
   // write cels on XML and PNG
   int index = 0;
   for (frame_t frame(0); frame<sprite->totalFrames(); ++frame) {
-    auto it = sprite->folder()->getLayerBegin(),
-         end = sprite->folder()->getLayerEnd();
-    for (; it != end; ++it, ++index) { // layers
-      Layer *layer = *it;
-
+    for (const Layer* layer : sprite->root()->layers()) { // layers
       int col = index % squareSide;
       int row = index / squareSide;
 
@@ -337,8 +326,8 @@ bool PixlyFormat::onSave(FileOp* fop)
         } // image
       } // cel
 
-      fop->setProgress(0.25 + 0.5 * (double)(index+1) / (double)imageCount);
-
+      fop->setProgress(0.1 + 0.8 * (double)(index+1) / (double)imageCount);
+      ++index;
     } // layer
   } // frame
 
diff --git a/src/app/flatten.cpp b/src/app/flatten.cpp
index ddd5be5db..45292b6b6 100644
--- a/src/app/flatten.cpp
+++ b/src/app/flatten.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -66,12 +66,9 @@ static bool has_cels(const Layer* layer, frame_t frame)
     case ObjectType::LayerImage:
       return (layer->cel(frame) ? true: false);
 
-    case ObjectType::LayerFolder: {
-      LayerConstIterator it = static_cast<const LayerFolder*>(layer)->getLayerBegin();
-      LayerConstIterator end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it) {
-        if (has_cels(*it, frame))
+    case ObjectType::LayerGroup: {
+      for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers()) {
+        if (has_cels(child, frame))
           return true;
       }
       break;
diff --git a/src/app/pref/preferences.h b/src/app/pref/preferences.h
index 944809ce4..7e154383c 100644
--- a/src/app/pref/preferences.h
+++ b/src/app/pref/preferences.h
@@ -21,7 +21,7 @@
 #include "doc/brush_pattern.h"
 #include "doc/documents_observer.h"
 #include "doc/frame.h"
-#include "doc/layer_index.h"
+#include "doc/layer_list.h"
 #include "filters/tiled_mode.h"
 #include "gfx/rect.h"
 #include "render/onionskin_position.h"
diff --git a/src/app/ui/document_view.cpp b/src/app/ui/document_view.cpp
index e3ae916f7..d56ed5c70 100644
--- a/src/app/ui/document_view.cpp
+++ b/src/app/ui/document_view.cpp
@@ -361,7 +361,7 @@ void DocumentView::onBeforeRemoveLayer(doc::DocumentEvent& ev)
 
   // If the layer that was removed is the selected one
   if (layer == m_editor->layer()) {
-    LayerFolder* parent = layer->parent();
+    LayerGroup* parent = layer->parent();
     Layer* layer_select = NULL;
 
     // Select previous layer, or next layer, or the parent (if it is
@@ -370,7 +370,7 @@ void DocumentView::onBeforeRemoveLayer(doc::DocumentEvent& ev)
       layer_select = layer->getPrevious();
     else if (layer->getNext())
       layer_select = layer->getNext();
-    else if (parent != sprite->folder())
+    else if (parent != sprite->root())
       layer_select = parent;
 
     m_editor->setLayer(layer_select);
diff --git a/src/app/ui/editor/brush_preview.cpp b/src/app/ui/editor/brush_preview.cpp
index 69068ecaf..b033c87d5 100644
--- a/src/app/ui/editor/brush_preview.cpp
+++ b/src/app/ui/editor/brush_preview.cpp
@@ -85,7 +85,9 @@ void BrushPreview::show(const gfx::Point& screenPos)
 
   app::Document* document = m_editor->document();
   Sprite* sprite = m_editor->sprite();
-  Layer* layer = m_editor->layer();
+  Layer* layer = (m_editor->layer() &&
+                  m_editor->layer()->isImage() ? m_editor->layer():
+                                                 nullptr);
   ASSERT(sprite);
 
   // Get drawable region
diff --git a/src/app/ui/editor/editor.cpp b/src/app/ui/editor/editor.cpp
index cc54e787c..75adcfddb 100644
--- a/src/app/ui/editor/editor.cpp
+++ b/src/app/ui/editor/editor.cpp
@@ -152,7 +152,7 @@ Editor::Editor(Document* document, EditorFlags flags)
   , m_decorator(NULL)
   , m_document(document)
   , m_sprite(m_document->sprite())
-  , m_layer(m_sprite->folder()->getFirstLayer())
+  , m_layer(m_sprite->root()->firstLayer())
   , m_frame(frame_t(0))
   , m_docPref(Preferences::instance().document(document))
   , m_brushPreview(this)
@@ -186,12 +186,16 @@ Editor::Editor(Document* document, EditorFlags flags)
       base::Bind<void>(&Editor::onContextBarBrushChange, this));
 
   // Restore last site in preferences
-  frame_t preferredFrame = m_docPref.site.frame();
-  Layer* preferredLayer = m_sprite->indexToLayer(m_docPref.site.layer());
-  if (preferredFrame >= 0 && preferredFrame <= m_sprite->lastFrame())
-    setFrame(preferredFrame);
-  if (preferredLayer)
-    setLayer(preferredLayer);
+  {
+    frame_t preferredFrame = m_docPref.site.frame();
+    if (preferredFrame >= 0 && preferredFrame <= m_sprite->lastFrame())
+      setFrame(preferredFrame);
+
+    LayerList layers = m_sprite->allBrowsableLayers();
+    layer_t layerIndex = m_docPref.site.layer();
+    if (layerIndex >= 0 && layerIndex < int(layers.size()))
+      setLayer(layers[layerIndex]);
+  }
 
   m_tiledConn = m_docPref.tiled.AfterChange.connect(base::Bind<void>(&Editor::invalidate, this));
   m_gridConn = m_docPref.grid.AfterChange.connect(base::Bind<void>(&Editor::invalidate, this));
@@ -211,8 +215,11 @@ Editor::Editor(Document* document, EditorFlags flags)
 Editor::~Editor()
 {
   if (m_document && m_sprite) {
+    LayerList layers = m_sprite->allBrowsableLayers();
+    layer_t layerIndex = doc::find_layer_index(layers, layer());
+
     m_docPref.site.frame(frame());
-    m_docPref.site.layer(m_sprite->layerToIndex(layer()));
+    m_docPref.site.layer(layerIndex);
   }
 
   m_observers.notifyDestroyEditor(this);
@@ -1442,8 +1449,8 @@ bool Editor::canDraw()
 {
   return (m_layer != NULL &&
           m_layer->isImage() &&
-          m_layer->isVisible() &&
-          m_layer->isEditable());
+          m_layer->isVisibleHierarchy() &&
+          m_layer->isEditableHierarchy());
 }
 
 bool Editor::isInsideSelection()
diff --git a/src/app/ui/editor/standby_state.cpp b/src/app/ui/editor/standby_state.cpp
index 33dc864f6..8e0b7d39b 100644
--- a/src/app/ui/editor/standby_state.cpp
+++ b/src/app/ui/editor/standby_state.cpp
@@ -209,11 +209,11 @@ bool StandbyState::onMouseDown(Editor* editor, MouseMessage* msg)
         StatusBar::instance()->showTip(1000,
           "The background layer cannot be moved");
       }
-      else if (!layer->isVisible()) {
+      else if (!layer->isVisibleHierarchy()) {
         StatusBar::instance()->showTip(1000,
           "Layer '%s' is hidden", layer->name().c_str());
       }
-      else if (!layer->isMovable() || !layer->isEditable()) {
+      else if (!layer->isMovable() || !layer->isEditableHierarchy()) {
         StatusBar::instance()->showTip(1000,
           "Layer '%s' is locked", layer->name().c_str());
       }
@@ -253,7 +253,7 @@ bool StandbyState::onMouseDown(Editor* editor, MouseMessage* msg)
         int x, y, opacity;
         Image* image = site.image(&x, &y, &opacity);
         if (layer && image) {
-          if (!layer->isEditable()) {
+          if (!layer->isEditableHierarchy()) {
             StatusBar::instance()->showTip(1000,
               "Layer '%s' is locked", layer->name().c_str());
             return true;
@@ -268,7 +268,7 @@ bool StandbyState::onMouseDown(Editor* editor, MouseMessage* msg)
 
     // Move selected pixels
     if (layer && editor->isInsideSelection() && msg->left()) {
-      if (!layer->isEditable()) {
+      if (!layer->isEditableHierarchy()) {
         StatusBar::instance()->showTip(1000,
           "Layer '%s' is locked", layer->name().c_str());
         return true;
@@ -297,7 +297,7 @@ bool StandbyState::onMouseDown(Editor* editor, MouseMessage* msg)
   }
 
   // Start the Tool-Loop
-  if (layer) {
+  if (layer && layer->isImage()) {
     // Disable layer edges to avoid showing the modified cel
     // information by ExpandCelCanvas (i.e. the cel origin is changed
     // to 0,0 coordinate.)
diff --git a/src/app/ui/editor/tool_loop_impl.cpp b/src/app/ui/editor/tool_loop_impl.cpp
index b637bb37f..cf26c2bfe 100644
--- a/src/app/ui/editor/tool_loop_impl.cpp
+++ b/src/app/ui/editor/tool_loop_impl.cpp
@@ -497,13 +497,13 @@ tools::ToolLoop* create_tool_loop(Editor* editor, Context* context)
         1000, "There is no active layer");
       return nullptr;
     }
-    else if (!layer->isVisible()) {
+    else if (!layer->isVisibleHierarchy()) {
       StatusBar::instance()->showTip(
         1000, "Layer '%s' is hidden", layer->name().c_str());
       return nullptr;
     }
     // If the active layer is read-only.
-    else if (!layer->isEditable()) {
+    else if (!layer->isEditableHierarchy()) {
       StatusBar::instance()->showTip(
         1000, "Layer '%s' is locked", layer->name().c_str());
       return nullptr;
@@ -615,8 +615,8 @@ tools::ToolLoop* create_tool_loop_preview(
 
   Layer* layer = editor->layer();
   if (!layer ||
-      !layer->isVisible() ||
-      !layer->isEditable()) {
+      !layer->isVisibleHierarchy() ||
+      !layer->isEditableHierarchy()) {
     return nullptr;
   }
 
diff --git a/src/app/ui/skin/skin_theme.cpp b/src/app/ui/skin/skin_theme.cpp
index 3e1854927..0f6a7f9fa 100644
--- a/src/app/ui/skin/skin_theme.cpp
+++ b/src/app/ui/skin/skin_theme.cpp
@@ -459,10 +459,10 @@ void SkinTheme::loadXml(const std::string& skinId)
         else if (ruleName == "icon") {
           if (align) (*style)[StyleSheet::iconAlignRule()] = css::Value(align);
           if (part_id) (*style)[StyleSheet::iconPartRule()] = css::Value(part_id);
+          if (color_id) (*style)[StyleSheet::iconColorRule()] = value_or_none(color_id);
 
           const char* x = xmlRule->Attribute("x");
           const char* y = xmlRule->Attribute("y");
-
           if (x) (*style)[StyleSheet::iconXRule()] = css::Value(strtol(x, NULL, 10));
           if (y) (*style)[StyleSheet::iconYRule()] = css::Value(strtol(y, NULL, 10));
         }
diff --git a/src/app/ui/skin/style.cpp b/src/app/ui/skin/style.cpp
index 2bbc28ceb..bb5d02269 100644
--- a/src/app/ui/skin/style.cpp
+++ b/src/app/ui/skin/style.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -23,6 +23,7 @@ namespace skin {
 css::State Style::m_hoverState("hover");
 css::State Style::m_activeState("active");
 css::State Style::m_clickedState("clicked");
+css::State Style::m_disabledState("disabled");
 
 Rule::~Rule()
 {
@@ -110,7 +111,10 @@ void IconRule::onPaint(ui::Graphics* g, const gfx::Rect& bounds, const char* tex
   x += m_x;
   y += m_y;
 
-  g->drawRgbaSurface(bmp, x, y);
+  if (m_color == gfx::ColorNone)
+    g->drawRgbaSurface(bmp, x, y);
+  else
+    g->drawColoredRgbaSurface(bmp, m_color, x, y);
 }
 
 Rules::Rules(const css::Query& query) :
@@ -125,6 +129,7 @@ Rules::Rules(const css::Query& query) :
   css::Value iconPart = query[StyleSheet::iconPartRule()];
   css::Value iconX = query[StyleSheet::iconXRule()];
   css::Value iconY = query[StyleSheet::iconYRule()];
+  css::Value iconColor = query[StyleSheet::iconColorRule()];
   css::Value textAlign = query[StyleSheet::textAlignRule()];
   css::Value textColor = query[StyleSheet::textColorRule()];
   css::Value paddingLeft = query[StyleSheet::paddingLeftRule()];
@@ -145,12 +150,14 @@ Rules::Rules(const css::Query& query) :
   if (iconAlign != none
     || iconPart != none
     || iconX != none
-    || iconY != none) {
+    || iconY != none
+    || iconColor != none) {
     m_icon = new IconRule();
     m_icon->setAlign((int)iconAlign.number());
     m_icon->setPart(StyleSheet::convertPart(iconPart));
     m_icon->setX((int)iconX.number()*ui::guiscale());
     m_icon->setY((int)iconY.number()*ui::guiscale());
+    m_icon->setColor(StyleSheet::convertColor(iconColor));
   }
 
   if (textAlign != none
diff --git a/src/app/ui/skin/style.h b/src/app/ui/skin/style.h
index ce677ecbe..af52034ab 100644
--- a/src/app/ui/skin/style.h
+++ b/src/app/ui/skin/style.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -84,12 +84,14 @@ namespace app {
 
     class IconRule : public Rule {
     public:
-      explicit IconRule() : m_align(0) { }
+      explicit IconRule() : m_align(0),
+                            m_color(gfx::ColorNone) { }
 
       void setAlign(int align) { m_align = align; }
       void setPart(const SkinPartPtr& part) { m_part = part; }
       void setX(int x) { m_x = x; }
       void setY(int y) { m_y = y; }
+      void setColor(gfx::Color color) { m_color = color; }
 
       SkinPartPtr getPart() { return m_part; }
 
@@ -100,6 +102,7 @@ namespace app {
       int m_align;
       SkinPartPtr m_part;
       int m_x, m_y;
+      gfx::Color m_color;
     };
 
     class Rules {
@@ -128,6 +131,7 @@ namespace app {
       static const css::State& hover() { return m_hoverState; }
       static const css::State& active() { return m_activeState; }
       static const css::State& clicked() { return m_clickedState; }
+      static const css::State& disabled() { return m_disabledState; }
 
       Style(css::Sheet& sheet, const std::string& id);
       ~Style();
@@ -156,6 +160,7 @@ namespace app {
       static css::State m_hoverState;
       static css::State m_activeState;
       static css::State m_clickedState;
+      static css::State m_disabledState;
     };
 
   } // namespace skin
diff --git a/src/app/ui/skin/style_sheet.cpp b/src/app/ui/skin/style_sheet.cpp
index 63d3c5dcd..c99323f39 100644
--- a/src/app/ui/skin/style_sheet.cpp
+++ b/src/app/ui/skin/style_sheet.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -28,6 +28,7 @@ css::Rule StyleSheet::m_iconAlignRule("icon-align");
 css::Rule StyleSheet::m_iconPartRule("icon-part");
 css::Rule StyleSheet::m_iconXRule("icon-x");
 css::Rule StyleSheet::m_iconYRule("icon-y");
+css::Rule StyleSheet::m_iconColorRule("icon-color");
 css::Rule StyleSheet::m_textAlignRule("text-align");
 css::Rule StyleSheet::m_textColorRule("text-color");
 css::Rule StyleSheet::m_paddingLeftRule("padding-left");
@@ -45,6 +46,7 @@ StyleSheet::StyleSheet()
   m_sheet->addRule(&m_iconPartRule);
   m_sheet->addRule(&m_iconXRule);
   m_sheet->addRule(&m_iconYRule);
+  m_sheet->addRule(&m_iconColorRule);
   m_sheet->addRule(&m_textAlignRule);
   m_sheet->addRule(&m_textColorRule);
   m_sheet->addRule(&m_paddingLeftRule);
diff --git a/src/app/ui/skin/style_sheet.h b/src/app/ui/skin/style_sheet.h
index 01bfc6926..e6cfaa39d 100644
--- a/src/app/ui/skin/style_sheet.h
+++ b/src/app/ui/skin/style_sheet.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -43,6 +43,7 @@ namespace app {
       static css::Rule& iconPartRule() { return m_iconPartRule; }
       static css::Rule& iconXRule() { return m_iconXRule; }
       static css::Rule& iconYRule() { return m_iconYRule; }
+      static css::Rule& iconColorRule() { return m_iconColorRule; }
       static css::Rule& textAlignRule() { return m_textAlignRule; }
       static css::Rule& textColorRule() { return m_textColorRule; }
       static css::Rule& paddingLeftRule() { return m_paddingLeftRule; }
@@ -69,6 +70,7 @@ namespace app {
       static css::Rule m_iconPartRule;
       static css::Rule m_iconXRule;
       static css::Rule m_iconYRule;
+      static css::Rule m_iconColorRule;
       static css::Rule m_textAlignRule;
       static css::Rule m_textColorRule;
       static css::Rule m_paddingLeftRule;
diff --git a/src/app/ui/status_bar.h b/src/app/ui/status_bar.h
index 8b9aa8e2e..40bb18a01 100644
--- a/src/app/ui/status_bar.h
+++ b/src/app/ui/status_bar.h
@@ -15,7 +15,6 @@
 #include "doc/context_observer.h"
 #include "doc/document_observer.h"
 #include "doc/documents_observer.h"
-#include "doc/layer_index.h"
 #include "ui/base.h"
 #include "ui/box.h"
 
diff --git a/src/app/ui/timeline.cpp b/src/app/ui/timeline.cpp
index a9ef00430..06a39cff4 100644
--- a/src/app/ui/timeline.cpp
+++ b/src/app/ui/timeline.cpp
@@ -118,6 +118,35 @@ struct Timeline::DrawCelData {
   CelIterator lastLink;         // Last link to the active cel
 };
 
+namespace {
+
+  template<typename Pred>
+  void for_each_expanded_layer(LayerGroup* group,
+                               Pred&& pred,
+                               int level = 0,
+                               LayerFlags flags =
+                                 LayerFlags(int(LayerFlags::Visible) |
+                                            int(LayerFlags::Editable))) {
+    if (!group->isVisible())
+      flags = static_cast<LayerFlags>(int(flags) & ~int(LayerFlags::Visible));
+
+    if (!group->isEditable())
+      flags = static_cast<LayerFlags>(int(flags) & ~int(LayerFlags::Editable));
+
+    for (Layer* child : group->layers()) {
+      if (child->isGroup() && !child->isCollapsed())
+        for_each_expanded_layer<Pred>(
+          static_cast<LayerGroup*>(child),
+          std::forward<Pred>(pred),
+          level+1,
+          flags);
+
+      pred(child, level, flags);
+    }
+  }
+
+} // anonymous namespace
+
 Timeline::Timeline()
   : Widget(kGenericWidget)
   , m_hbar(HORIZONTAL, this)
@@ -171,7 +200,7 @@ void Timeline::updateUsingEditor(Editor* editor)
   detachDocument();
 
   if (m_range.enabled()) {
-    m_range.disableRange();
+    m_range.clearRange();
     invalidate();
   }
 
@@ -233,6 +262,23 @@ bool Timeline::isMovingCel() const
           m_range.type() == Range::kCels);
 }
 
+bool Timeline::selectedLayersBounds(const SelectedLayers& layers,
+                                    layer_t* first, layer_t* last) const
+{
+  if (layers.empty())
+    return false;
+
+  *first = *last = getLayerIndex(*layers.begin());
+
+  for (auto layer : layers) {
+    layer_t i = getLayerIndex(layer);
+    if (*first > i) *first = i;
+    if (*last < i) *last = i;
+  }
+
+  return true;
+}
+
 void Timeline::setLayer(Layer* layer)
 {
   ASSERT(m_editor != NULL);
@@ -274,23 +320,50 @@ void Timeline::prepareToMoveRange()
 {
   ASSERT(m_range.enabled());
 
-  m_moveRangeData.activeRelativeLayer = getLayerIndex(m_layer) - m_range.layerBegin();
-  m_moveRangeData.activeRelativeFrame = m_frame - m_range.frameBegin();
+  layer_t i = 0;
+  for (auto layer : m_range.selectedLayers().toLayerList()) {
+    if (layer == m_layer)
+      break;
+    ++i;
+  }
+
+  frame_t j = 0;
+  for (auto frame : m_range.selectedFrames()) {
+    if (frame == m_frame)
+      break;
+    ++j;
+  }
+
+  m_moveRangeData.activeRelativeLayer = i;
+  m_moveRangeData.activeRelativeFrame = j;
 }
 
 void Timeline::moveRange(Range& range)
 {
   regenerateLayers();
 
-  if (range.layerBegin() >= LayerIndex(0) &&
-      range.layerBegin() + m_moveRangeData.activeRelativeLayer < int(m_layers.size())) {
-    setLayer(m_layers[range.layerBegin() + m_moveRangeData.activeRelativeLayer]);
+  // We have to change the range before we generate an
+  // onActiveSiteChange() event so observers (like cel properties
+  // dialog) know the new selected range.
+  m_range = range;
+
+  layer_t i = 0;
+  for (auto layer : range.selectedLayers().toLayerList()) {
+    if (i == m_moveRangeData.activeRelativeLayer) {
+      setLayer(layer);
+      break;
+    }
+    ++i;
   }
 
-  if (range.frameBegin() >= frame_t(0))
-    setFrame(range.frameBegin() + m_moveRangeData.activeRelativeFrame, true);
-
-  m_range = range;
+  frame_t j = 0;
+  for (auto frame : range.selectedFrames()) {
+    if (j == m_moveRangeData.activeRelativeFrame) {
+      setFrame(frame, true);
+      break;
+    }
+    ++j;
+  }
 }
 
 void Timeline::activateClipboardRange()
@@ -351,6 +424,14 @@ bool Timeline::onProcessMessage(Message* msg)
       // Clicked-part = hot-part.
       m_clk = m_hot;
 
+      // With Ctrl+click (Win/Linux) or Shift+click (OS X) we can
+      // select non-adjacents layer/frame ranges
+      bool clearRange =
+#if !defined(__APPLE__)
+        !msg->ctrlPressed() ||
+#endif
+        !msg->shiftPressed();
+
       captureMouse();
 
       switch (m_hot.part) {
@@ -372,7 +453,10 @@ bool Timeline::onProcessMessage(Message* msg)
 
           if (selectFrame) {
             m_state = STATE_SELECTING_FRAMES;
-            m_range.startRange(getLayerIndex(m_layer), m_clk.frame, Range::kFrames);
+            if (clearRange)
+              m_range.clearRange();
+            m_range.startRange(m_layer, m_clk.frame, Range::kFrames);
+            m_startRange = m_range;
 
             setFrame(m_clk.frame, true);
           }
@@ -380,16 +464,20 @@ bool Timeline::onProcessMessage(Message* msg)
         }
         case PART_LAYER_TEXT: {
           base::ScopedValue<bool> lock(m_fromTimeline, true, false);
-          LayerIndex old_layer = getLayerIndex(m_layer);
+          layer_t old_layer = getLayerIndex(m_layer);
           bool selectLayer = (mouseMsg->left() || !isLayerActive(m_clk.layer));
 
           if (selectLayer) {
             m_state = STATE_SELECTING_LAYERS;
-            m_range.startRange(m_clk.layer, m_frame, Range::kLayers);
+            if (clearRange)
+              m_range.clearRange();
+            m_range.startRange(m_layers[m_clk.layer].layer,
+                               m_frame, Range::kLayers);
+            m_startRange = m_range;
 
             // Did the user select another layer?
             if (old_layer != m_clk.layer) {
-              setLayer(m_layers[m_clk.layer]);
+              setLayer(m_layers[m_clk.layer].layer);
               invalidate();
             }
           }
@@ -406,7 +494,7 @@ bool Timeline::onProcessMessage(Message* msg)
           break;
         case PART_CEL: {
           base::ScopedValue<bool> lock(m_fromTimeline, true, false);
-          LayerIndex old_layer = getLayerIndex(m_layer);
+          layer_t old_layer = getLayerIndex(m_layer);
           bool selectCel = (mouseMsg->left()
             || !isLayerActive(m_clk.layer)
             || !isFrameActive(m_clk.frame));
@@ -414,13 +502,16 @@ bool Timeline::onProcessMessage(Message* msg)
 
           if (selectCel) {
             m_state = STATE_SELECTING_CELS;
-            m_range.startRange(m_clk.layer, m_clk.frame, Range::kCels);
+            m_range.clearRange();
+            m_range.startRange(m_layers[m_clk.layer].layer,
+                               m_clk.frame, Range::kCels);
+            m_startRange = m_range;
           }
 
           // Select the new clicked-part.
           if (old_layer != m_clk.layer
             || old_frame != m_clk.frame) {
-            setLayer(m_layers[m_clk.layer]);
+            setLayer(m_layers[m_clk.layer].layer);
             setFrame(m_clk.frame, true);
             invalidate();
           }
@@ -440,15 +531,20 @@ bool Timeline::onProcessMessage(Message* msg)
           if (m_range.type() == Range::kCels) {
             m_clk = hitTestCel(mouseMsg->position() - bounds().origin());
 
-            if (m_clk.layer < m_range.layerBegin())
-              m_clk.layer = m_range.layerBegin();
-            else if (m_clk.layer > m_range.layerEnd())
-              m_clk.layer = m_range.layerEnd();
+            if (m_range.layers() > 0) {
+              layer_t layerFirst, layerLast;
+              if (selectedLayersBounds(selectedLayers(),
+                                       &layerFirst, &layerLast)) {
+                layer_t layerIdx = m_clk.layer;
+                layerIdx = MID(layerFirst, layerIdx, layerLast);
+                m_clk.layer = layerIdx;
+              }
+            }
 
-            if (m_clk.frame < m_range.frameBegin())
-              m_clk.frame = m_range.frameBegin();
-            else if (m_clk.frame > m_range.frameEnd())
-              m_clk.frame = m_range.frameEnd();
+            if (m_clk.frame < m_range.firstFrame())
+              m_clk.frame = m_range.firstFrame();
+            else if (m_clk.frame > m_range.lastFrame())
+              m_clk.frame = m_range.lastFrame();
           }
           break;
       }
@@ -520,24 +616,38 @@ bool Timeline::onProcessMessage(Message* msg)
         switch (m_state) {
 
           case STATE_SELECTING_LAYERS: {
-            if (m_layer != m_layers[hit.layer]) {
-              m_range.endRange(hit.layer, m_frame);
-              setLayer(m_layers[m_clk.layer = hit.layer]);
+            Layer* hitLayer = m_layers[hit.layer].layer;
+            if (m_layer != hitLayer) {
+              m_clk.layer = hit.layer;
+
+              // We have to change the range before we generate an
+              // onActiveSiteChange() event so observers (like cel
+              // properties dialog) know the new selected range.
+              m_range = m_startRange;
+              m_range.endRange(hitLayer, m_frame);
+
+              setLayer(hitLayer);
             }
             break;
           }
 
           case STATE_SELECTING_FRAMES: {
-            m_range.endRange(getLayerIndex(m_layer), hit.frame);
+            m_range = m_startRange;
+            m_range.endRange(m_layer, hit.frame);
+
             setFrame(m_clk.frame = hit.frame, true);
             break;
           }
 
           case STATE_SELECTING_CELS:
-            if ((m_layer != m_layers[hit.layer])
-              || (m_frame != hit.frame)) {
-              m_range.endRange(hit.layer, hit.frame);
-              setLayer(m_layers[m_clk.layer = hit.layer]);
+            Layer* hitLayer = m_layers[hit.layer].layer;
+            if ((m_layer != hitLayer) || (m_frame != hit.frame)) {
+              m_clk.layer = hit.layer;
+
+              m_range = m_startRange;
+              m_range.endRange(hitLayer, hit.frame);
+
+              setLayer(hitLayer);
               setFrame(m_clk.frame = hit.frame, true);
             }
             break;
@@ -560,6 +670,7 @@ bool Timeline::onProcessMessage(Message* msg)
           return true;
         }
 
+        bool regenLayers = false;
         setHot(hitTest(msg, mouseMsg->position() - bounds().origin()));
 
         switch (m_hot.part) {
@@ -571,9 +682,18 @@ bool Timeline::onProcessMessage(Message* msg)
             break;
 
           case PART_HEADER_EYE: {
+            ASSERT(m_sprite);
+            if (!m_sprite)
+              break;
+
             bool newVisibleState = !allLayersVisible();
-            for (size_t i=0; i<m_layers.size(); i++)
-              m_layers[i]->setVisible(newVisibleState);
+            for (Layer* topLayer : m_sprite->root()->layers()) {
+              if (topLayer->isVisible() != newVisibleState) {
+                topLayer->setVisible(newVisibleState);
+                if (topLayer->isGroup())
+                  regenLayers = true;
+              }
+            }
 
             // Redraw all views.
             m_document->notifyGeneralUpdate();
@@ -581,16 +701,25 @@ bool Timeline::onProcessMessage(Message* msg)
           }
 
           case PART_HEADER_PADLOCK: {
+            ASSERT(m_sprite);
+            if (!m_sprite)
+              break;
+
             bool newEditableState = !allLayersUnlocked();
-            for (size_t i=0; i<m_layers.size(); i++)
-              m_layers[i]->setEditable(newEditableState);
+            for (Layer* topLayer : m_sprite->root()->layers()) {
+              if (topLayer->isEditable() != newEditableState) {
+                topLayer->setEditable(newEditableState);
+                if (topLayer->isGroup())
+                  regenLayers = true;
+              }
+            }
             break;
           }
 
           case PART_HEADER_CONTINUOUS: {
             bool newContinuousState = !allLayersContinuous();
             for (size_t i=0; i<m_layers.size(); i++)
-              m_layers[i]->setContinuous(newContinuousState);
+              m_layers[i].layer->setContinuous(newContinuousState);
             break;
           }
 
@@ -657,9 +786,27 @@ bool Timeline::onProcessMessage(Message* msg)
           case PART_LAYER_EYE_ICON:
             // Hide/show layer.
             if (m_hot.layer == m_clk.layer && validLayer(m_hot.layer)) {
-              Layer* layer = m_layers[m_clk.layer];
-              ASSERT(layer != NULL);
-              layer->setVisible(!layer->isVisible());
+              LayerInfo& info = m_layers[m_clk.layer];
+              Layer* layer = info.layer;
+              ASSERT(layer);
+
+              // Show parents
+              if (!info.parentVisible()) {
+                regenLayers = true;
+
+                layer->setVisible(true);
+                layer = layer->parent();
+                while (layer) {
+                  if (!layer->isVisible())
+                    layer->setVisible(true);
+                  layer = layer->parent();
+                }
+              }
+              else {
+                layer->setVisible(!layer->isVisible());
+                if (layer->isGroup() && layer->isExpanded())
+                  regenLayers = true;
+              }
 
               // Redraw all views.
               m_document->notifyGeneralUpdate();
@@ -669,17 +816,48 @@ bool Timeline::onProcessMessage(Message* msg)
           case PART_LAYER_PADLOCK_ICON:
             // Lock/unlock layer.
             if (m_hot.layer == m_clk.layer && validLayer(m_hot.layer)) {
-              Layer* layer = m_layers[m_clk.layer];
-              ASSERT(layer != NULL);
-              layer->setEditable(!layer->isEditable());
+              LayerInfo& info = m_layers[m_clk.layer];
+              Layer* layer = info.layer;
+              ASSERT(layer);
+
+              // Unlock parents
+              if (!info.parentEditable()) {
+                regenLayers = true;
+
+                layer->setEditable(true);
+                layer = layer->parent();
+                while (layer) {
+                  if (!layer->isEditable())
+                    layer->setEditable(true);
+                  layer = layer->parent();
+                }
+              }
+              else {
+                layer->setEditable(!layer->isEditable());
+                if (layer->isGroup() && layer->isExpanded())
+                  regenLayers = true;
+              }
             }
             break;
 
           case PART_LAYER_CONTINUOUS_ICON:
             if (m_hot.layer == m_clk.layer && validLayer(m_hot.layer)) {
-              Layer* layer = m_layers[m_clk.layer];
-              ASSERT(layer != NULL);
-              layer->setContinuous(!layer->isContinuous());
+              Layer* layer = m_layers[m_clk.layer].layer;
+              ASSERT(layer);
+              if (layer) {
+                if (layer->isImage())
+                  layer->setContinuous(!layer->isContinuous());
+                else if (layer->isGroup()) {
+                  layer->setCollapsed(!layer->isCollapsed());
+
+                  regenerateLayers();
+                  showCurrentCel();
+                  invalidate();
+
+                  updateByMousePos(
+                    msg, ui::get_mouse_position() - bounds().origin());
+                }
+              }
             }
             break;
 
@@ -739,6 +917,11 @@ bool Timeline::onProcessMessage(Message* msg)
 
         }
 
+        if (regenLayers) {
+          regenerateLayers();
+          invalidate();
+        }
+
         if (m_state == STATE_MOVING_RANGE &&
             m_dropRange.type() != Range::kNone) {
           dropRange(isCopyKeyPressed(mouseMsg) ?
@@ -803,7 +986,7 @@ bool Timeline::onProcessMessage(Message* msg)
 
         case kKeyEsc:
           if (m_state == STATE_STANDBY) {
-            m_range.disableRange();
+            m_range.clearRange();
             invalidate();
           }
           else {
@@ -928,11 +1111,11 @@ void Timeline::onPaint(ui::PaintEvent& ev)
     // Lock the sprite to read/render it.
     const DocumentReader documentReader(m_document, 0);
 
-    LayerIndex layer, first_layer, last_layer;
-    frame_t frame, first_frame, last_frame;
+    layer_t layer, firstLayer, lastLayer;
+    frame_t frame, firstFrame, lastFrame;
 
-    getDrawableLayers(g, &first_layer, &last_layer);
-    getDrawableFrames(g, &first_frame, &last_frame);
+    getDrawableLayers(g, &firstLayer, &lastLayer);
+    getDrawableFrames(g, &firstFrame, &lastFrame);
 
     drawTop(g);
 
@@ -943,7 +1126,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
     {
       IntersectClip clip(g, getFrameHeadersBounds());
       if (clip) {
-        for (frame=first_frame; frame<=last_frame; ++frame)
+        for (frame=firstFrame; frame<=lastFrame; ++frame)
           drawHeaderFrame(g, frame);
 
         // Draw onionskin indicators.
@@ -958,7 +1141,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
 
     // Draw each visible layer.
     DrawCelData data;
-    for (layer=last_layer; layer>=first_layer; --layer) {
+    for (layer=lastLayer; layer>=firstLayer; --layer) {
       {
         IntersectClip clip(g, getLayerHeadersBounds());
         if (clip)
@@ -969,11 +1152,20 @@ void Timeline::onPaint(ui::PaintEvent& ev)
       if (!clip)
         continue;
 
+      Layer* layerPtr = m_layers[layer].layer;
+      if (!layerPtr->isImage()) {
+        // Draw empty cels
+        for (frame=firstFrame; frame<=lastFrame; ++frame) {
+          drawCel(g, layer, frame, nullptr, nullptr);
+        }
+        continue;
+      }
+
       // Get the first CelIterator to be drawn (it is the first cel with cel->frame >= first_frame)
-      LayerImage* layerPtr = static_cast<LayerImage*>(m_layers[layer]);
-      data.begin = layerPtr->getCelBegin();
-      data.end = layerPtr->getCelEnd();
-      data.it = layerPtr->findFirstCelIteratorAfter(first_frame-1);
+      LayerImage* layerImagePtr = static_cast<LayerImage*>(layerPtr);
+      data.begin = layerImagePtr->getCelBegin();
+      data.end = layerImagePtr->getCelEnd();
+      data.it = layerImagePtr->findFirstCelIteratorAfter(firstFrame-1);
       data.prevIt = data.end;
       data.nextIt = (data.it != data.end ? data.it+1: data.end);
 
@@ -982,7 +1174,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
       data.lastLink = data.end;
 
       if (layerPtr == m_layer) {
-        data.activeIt = layerPtr->findCelIterator(m_frame);
+        data.activeIt = layerImagePtr->findCelIterator(m_frame);
         if (data.activeIt != data.end) {
           data.firstLink = data.activeIt;
           data.lastLink = data.activeIt;
@@ -995,7 +1187,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
               --it2;
               if ((*it2)->image()->id() == imageId) {
                 data.firstLink = it2;
-                if ((*data.firstLink)->frame() < first_frame)
+                if ((*data.firstLink)->frame() < firstFrame)
                   break;
               }
             } while (it2 != data.begin);
@@ -1005,7 +1197,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
           while (it2 != data.end) {
             if ((*it2)->image()->id() == imageId) {
               data.lastLink = it2;
-              if ((*data.lastLink)->frame() > last_frame)
+              if ((*data.lastLink)->frame() > lastFrame)
                 break;
             }
             ++it2;
@@ -1016,7 +1208,7 @@ void Timeline::onPaint(ui::PaintEvent& ev)
         data.activeIt = data.end;
 
       // Draw every visible cel for each layer.
-      for (frame=first_frame; frame<=last_frame; ++frame) {
+      for (frame=firstFrame; frame<=lastFrame; ++frame) {
         Cel* cel =
           (data.it != data.end &&
            (*data.it)->frame() == frame ? *data.it: nullptr);
@@ -1094,7 +1286,7 @@ void Timeline::onAfterRemoveLayer(doc::DocumentEvent& ev)
 
   // If the layer that was removed is the selected one
   if (layer == getLayer()) {
-    LayerFolder* parent = layer->parent();
+    LayerGroup* parent = layer->parent();
     Layer* layer_select = NULL;
 
     // Select previous layer, or next layer, or the parent (if it is
@@ -1103,7 +1295,7 @@ void Timeline::onAfterRemoveLayer(doc::DocumentEvent& ev)
       layer_select = layer->getPrevious();
     else if (layer->getNext())
       layer_select = layer->getNext();
-    else if (parent != sprite->folder())
+    else if (parent != sprite->root())
       layer_select = parent;
 
     setLayer(layer_select);
@@ -1144,7 +1336,7 @@ void Timeline::onRemoveFrame(doc::DocumentEvent& ev)
 
 void Timeline::onSelectionChanged(doc::DocumentEvent& ev)
 {
-  m_range.disableRange();
+  m_range.clearRange();
   invalidate();
 }
 
@@ -1166,7 +1358,7 @@ void Timeline::onAfterFrameChanged(Editor* editor)
   setFrame(editor->frame(), false);
 
   if (!hasCapture())
-    m_range.disableRange();
+    m_range.clearRange();
 
   showCurrentCel();
   invalidate();
@@ -1177,10 +1369,10 @@ void Timeline::onAfterLayerChanged(Editor* editor)
   if (m_fromTimeline)
     return;
 
-  setLayer(editor->layer());
-
   if (!hasCapture())
-    m_range.disableRange();
+    m_range.clearRange();
+
+  setLayer(editor->layer());
 
   showCurrentCel();
   invalidate();
@@ -1231,33 +1423,36 @@ void Timeline::setCursor(ui::Message* msg, const Hit& hit)
   }
 }
 
-void Timeline::getDrawableLayers(ui::Graphics* g, LayerIndex* first_layer, LayerIndex* last_layer)
+void Timeline::getDrawableLayers(ui::Graphics* g, layer_t* firstLayer, layer_t* lastLayer)
 {
   int hpx = (clientBounds().h - HDRSIZE - topHeight());
-  LayerIndex i = lastLayer() - LayerIndex((viewScroll().y+hpx) / LAYSIZE);
-  i = MID(firstLayer(), i, lastLayer());
+  layer_t i = this->lastLayer() - ((viewScroll().y+hpx) / LAYSIZE);
+  i = MID(this->firstLayer(), i, this->lastLayer());
 
-  LayerIndex j = i + LayerIndex(hpx / LAYSIZE + 1);
+  layer_t j = i + (hpx / LAYSIZE + 1);
   if (!m_layers.empty())
-    j = MID(firstLayer(), j, lastLayer());
+    j = MID(this->firstLayer(), j, this->lastLayer());
   else
-    j = LayerIndex::NoLayer;
+    j = -1;
 
-  *first_layer = i;
-  *last_layer = j;
+  *firstLayer = i;
+  *lastLayer = j;
 }
 
-void Timeline::getDrawableFrames(ui::Graphics* g, frame_t* first_frame, frame_t* last_frame)
+void Timeline::getDrawableFrames(ui::Graphics* g, frame_t* firstFrame, frame_t* lastFrame)
 {
   int availW = (clientBounds().w - m_separator_x);
 
-  *first_frame = frame_t(viewScroll().x / FRMSIZE);
-  *last_frame = *first_frame + frame_t(availW / FRMSIZE) + ((availW % FRMSIZE) > 0 ? 1: 0);
+  *firstFrame = frame_t(viewScroll().x / FRMSIZE);
+  *lastFrame = *firstFrame + frame_t(availW / FRMSIZE) + ((availW % FRMSIZE) > 0 ? 1: 0);
 }
 
 void Timeline::drawPart(ui::Graphics* g, const gfx::Rect& bounds,
-  const char* text, Style* style,
-  bool is_active, bool is_hover, bool is_clicked)
+                        const char* text, Style* style,
+                        bool is_active,
+                        bool is_hover,
+                        bool is_clicked,
+                        bool is_disabled)
 {
   IntersectClip clip(g, bounds);
   if (!clip)
@@ -1267,6 +1462,7 @@ void Timeline::drawPart(ui::Graphics* g, const gfx::Rect& bounds,
   if (is_active) state += Style::active();
   if (is_hover) state += Style::hover();
   if (is_clicked) state += Style::clicked();
+  if (is_disabled) state += Style::disabled();
 
   style->paint(g, bounds, text, state);
 }
@@ -1361,10 +1557,10 @@ void Timeline::drawHeaderFrame(ui::Graphics* g, frame_t frame)
   g->setFont(oldFont);
 }
 
-void Timeline::drawLayer(ui::Graphics* g, LayerIndex layerIdx)
+void Timeline::drawLayer(ui::Graphics* g, int layerIdx)
 {
   SkinTheme::Styles& styles = skinTheme()->styles;
-  Layer* layer = m_layers[layerIdx];
+  Layer* layer = m_layers[layerIdx].layer;
   bool is_active = isLayerActive(layerIdx);
   bool hotlayer = (m_hot.layer == layerIdx);
   bool clklayer = (m_clk.layer == layerIdx);
@@ -1375,39 +1571,63 @@ void Timeline::drawLayer(ui::Graphics* g, LayerIndex layerIdx)
 
   // Draw the eye (visible flag).
   bounds = getPartBounds(Hit(PART_LAYER_EYE_ICON, layerIdx));
-  drawPart(g, bounds, NULL,
-    layer->isVisible() ? styles.timelineOpenEye(): styles.timelineClosedEye(),
+  drawPart(
+    g, bounds, nullptr,
+    (layer->isVisible() ? styles.timelineOpenEye():
+                          styles.timelineClosedEye()),
     is_active,
     (hotlayer && m_hot.part == PART_LAYER_EYE_ICON),
-    (clklayer && m_clk.part == PART_LAYER_EYE_ICON));
+    (clklayer && m_clk.part == PART_LAYER_EYE_ICON),
+    !m_layers[layerIdx].parentVisible());
 
   // Draw the padlock (editable flag).
   bounds = getPartBounds(Hit(PART_LAYER_PADLOCK_ICON, layerIdx));
-  drawPart(g, bounds, NULL,
-    layer->isEditable() ? styles.timelineOpenPadlock(): styles.timelineClosedPadlock(),
+  drawPart(
+    g, bounds, nullptr,
+    (layer->isEditable() ? styles.timelineOpenPadlock():
+                           styles.timelineClosedPadlock()),
     is_active,
     (hotlayer && m_hot.part == PART_LAYER_PADLOCK_ICON),
-    (clklayer && m_clk.part == PART_LAYER_PADLOCK_ICON));
+    (clklayer && m_clk.part == PART_LAYER_PADLOCK_ICON),
+    !m_layers[layerIdx].parentEditable());
 
-  // Draw the continuous flag.
+  // Draw the continuous flag/group icon.
   bounds = getPartBounds(Hit(PART_LAYER_CONTINUOUS_ICON, layerIdx));
-  drawPart(g, bounds, NULL,
-    layer->isContinuous() ? styles.timelineContinuous(): styles.timelineDiscontinuous(),
-    is_active,
-    (hotlayer && m_hot.part == PART_LAYER_CONTINUOUS_ICON),
-    (clklayer && m_clk.part == PART_LAYER_CONTINUOUS_ICON));
+  if (layer->isImage()) {
+    drawPart(g, bounds, NULL,
+             layer->isContinuous() ? styles.timelineContinuous():
+                                     styles.timelineDiscontinuous(),
+             is_active,
+             (hotlayer && m_hot.part == PART_LAYER_CONTINUOUS_ICON),
+             (clklayer && m_clk.part == PART_LAYER_CONTINUOUS_ICON));
+  }
+  else if (layer->isGroup()) {
+    drawPart(g, bounds, NULL,
+             layer->isCollapsed() ? styles.timelineClosedGroup():
+                                    styles.timelineOpenGroup(),
+             is_active,
+             (hotlayer && m_hot.part == PART_LAYER_CONTINUOUS_ICON),
+             (clklayer && m_clk.part == PART_LAYER_CONTINUOUS_ICON));
+  }
 
   // Get the layer's name bounds.
   bounds = getPartBounds(Hit(PART_LAYER_TEXT, layerIdx));
 
   // Draw layer name.
   doc::color_t layerColor = layer->userData().color();
-  if (doc::rgba_geta(layerColor) > 0) {
-    drawPart(g, bounds, nullptr, styles.timelineLayer(),
-             is_active,
-             (hotlayer && m_hot.part == PART_LAYER_TEXT),
-             (clklayer && m_clk.part == PART_LAYER_TEXT));
+  gfx::Rect textBounds = bounds;
+  if (m_layers[layerIdx].level > 0) {
+    int w = m_layers[layerIdx].level*FRMSIZE;
+    textBounds.x += w;
+    textBounds.w -= w;
+  }
 
+  drawPart(g, bounds, nullptr, styles.timelineLayer(),
+           is_active,
+           (hotlayer && m_hot.part == PART_LAYER_TEXT),
+           (clklayer && m_clk.part == PART_LAYER_TEXT));
+
+  if (doc::rgba_geta(layerColor) > 0) {
     // Fill with an user-defined custom color.
     auto b2 = bounds;
     b2.shrink(1*guiscale()).inflate(1*guiscale());
@@ -1417,13 +1637,13 @@ void Timeline::drawLayer(ui::Graphics* g, LayerIndex layerIdx)
                           doc::rgba_geta(layerColor)),
                 b2);
 
-    drawPart(g, bounds, layer->name().c_str(), styles.timelineLayerTextOnly(),
+    drawPart(g, textBounds, layer->name().c_str(), styles.timelineLayerTextOnly(),
              is_active,
              (hotlayer && m_hot.part == PART_LAYER_TEXT),
              (clklayer && m_clk.part == PART_LAYER_TEXT));
   }
   else {
-    drawPart(g, bounds, layer->name().c_str(), styles.timelineLayer(),
+    drawPart(g, textBounds, layer->name().c_str(), styles.timelineLayer(),
              is_active,
              (hotlayer && m_hot.part == PART_LAYER_TEXT),
              (clklayer && m_clk.part == PART_LAYER_TEXT));
@@ -1451,16 +1671,17 @@ void Timeline::drawLayer(ui::Graphics* g, LayerIndex layerIdx)
   }
 }
 
-void Timeline::drawCel(ui::Graphics* g, LayerIndex layerIndex, frame_t frame, Cel* cel, DrawCelData* data)
+void Timeline::drawCel(ui::Graphics* g, layer_t layerIndex, frame_t frame, Cel* cel, DrawCelData* data)
 {
   SkinTheme::Styles& styles = skinTheme()->styles;
-  LayerImage* layer = static_cast<LayerImage*>(m_layers[layerIndex]);
-  Image* image = (cel ? cel->image(): NULL);
+  Layer* layer = m_layers[layerIndex].layer;
+  Image* image = (cel ? cel->image(): nullptr);
   bool is_hover = (m_hot.part == PART_CEL &&
     m_hot.layer == layerIndex &&
     m_hot.frame == frame);
-  bool is_active = (isLayerActive(layerIndex) || isFrameActive(frame));
-  bool is_empty = (image == NULL);
+  const bool is_active = (isLayerActive(layerIndex) ||
+                          isFrameActive(frame));
+  const bool is_empty = (image == nullptr);
   gfx::Rect bounds = getPartBounds(Hit(PART_CEL, layerIndex, frame));
   IntersectClip clip(g, bounds);
   if (!clip)
@@ -1488,7 +1709,7 @@ void Timeline::drawCel(ui::Graphics* g, LayerIndex layerIndex, frame_t frame, Ce
   skin::Style* style;
   bool fromLeft = false;
   bool fromRight = false;
-  if (is_empty) {
+  if (is_empty || !data) {
     style = styles.timelineEmptyFrame();
   }
   else {
@@ -1516,7 +1737,7 @@ void Timeline::drawCel(ui::Graphics* g, LayerIndex layerIndex, frame_t frame, Ce
   drawPart(g, bounds, NULL, style, is_active, is_hover);
 
   // Draw decorators to link the activeCel with its links.
-  if (data->activeIt != data->end)
+  if (data && data->activeIt != data->end)
     drawCelLinkDecorators(g, bounds, cel, frame, is_active, is_hover, data);
 }
 
@@ -1577,7 +1798,7 @@ void Timeline::drawFrameTags(ui::Graphics* g)
     }
 
     {
-      bounds = getPartBounds(Hit(PART_FRAME_TAG, LayerIndex(0), 0, frameTag->id()));
+      bounds = getPartBounds(Hit(PART_FRAME_TAG, 0, 0, frameTag->id()));
 
       gfx::Color bg = frameTag->color();
       if (m_clk.part == PART_FRAME_TAG && m_clk.frameTag == frameTag->id()) {
@@ -1891,18 +2112,26 @@ gfx::Rect Timeline::getRangeBounds(const Range& range) const
 {
   gfx::Rect rc;
   switch (range.type()) {
-    case Range::kNone: break; // Return empty rectangle
+    case Range::kNone:
+      // Return empty rectangle
+      break;
     case Range::kCels:
-      rc = getPartBounds(Hit(PART_CEL, range.layerBegin(), range.frameBegin())).createUnion(
-        getPartBounds(Hit(PART_CEL, range.layerEnd(), range.frameEnd())));
+      for (auto layer : range.selectedLayers()) {
+        layer_t layerIdx = getLayerIndex(layer);
+        for (auto frame : range.selectedFrames())
+          rc |= getPartBounds(Hit(PART_CEL, layerIdx, frame));
+      }
       break;
-    case Range::kFrames:
-      rc = getPartBounds(Hit(PART_HEADER_FRAME, firstLayer(), range.frameBegin())).createUnion(
-        getPartBounds(Hit(PART_HEADER_FRAME, firstLayer(), range.frameEnd())));
+    case Range::kFrames: {
+      for (auto frame : range.selectedFrames())
+        rc |= getPartBounds(Hit(PART_HEADER_FRAME, 0, frame));
       break;
+    }
     case Range::kLayers:
-      rc = getPartBounds(Hit(PART_LAYER, range.layerBegin())).createUnion(
-        getPartBounds(Hit(PART_LAYER, range.layerEnd())));
+      for (auto layer : range.selectedLayers()) {
+        layer_t layerIdx = getLayerIndex(layer);
+        rc |= getPartBounds(Hit(PART_LAYER, layerIdx));
+      }
       break;
   }
   return rc;
@@ -1915,19 +2144,29 @@ void Timeline::invalidateHit(const Hit& hit)
 
 void Timeline::regenerateLayers()
 {
-  ASSERT(m_document != NULL);
-  ASSERT(m_sprite != NULL);
+  ASSERT(m_document);
+  ASSERT(m_sprite);
+
+  size_t nlayers = 0;
+  for_each_expanded_layer(
+    m_sprite->root(),
+    [&nlayers](Layer* layer, int level, LayerFlags flags) {
+      ++nlayers;
+    });
 
-  size_t nlayers = m_sprite->countLayers();
   if (m_layers.size() != nlayers) {
     if (nlayers > 0)
-      m_layers.resize(nlayers, NULL);
+      m_layers.resize(nlayers);
     else
       m_layers.clear();
   }
 
-  for (size_t c=0; c<nlayers; c++)
-    m_layers[c] = m_sprite->indexToLayer(LayerIndex(c));
+  size_t i = 0;
+  for_each_expanded_layer(
+    m_sprite->root(),
+    [&i, this](Layer* layer, int level, LayerFlags flags) {
+      m_layers[i++] = LayerInfo(layer, level, flags);
+    });
 
   updateScrollBars();
 }
@@ -1952,11 +2191,7 @@ void Timeline::updateByMousePos(ui::Message* msg, const gfx::Point& mousePos)
 
 Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
 {
-  Hit hit(
-    PART_NOTHING,
-    LayerIndex::NoLayer,
-    frame_t(-1));
-
+  Hit hit(PART_NOTHING, -1, -1);
   if (!m_document)
     return hit;
 
@@ -1967,8 +2202,8 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
     gfx::Point scroll = viewScroll();
     int top = topHeight();
 
-    hit.layer = lastLayer() - LayerIndex(
-      (mousePos.y
+    hit.layer = lastLayer() -
+      ((mousePos.y
         - top
         - HDRSIZE
         + scroll.y) / LAYSIZE);
@@ -1978,6 +2213,10 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
         - m_separator_w
         + scroll.x) / FRMSIZE);
 
+    // Flag which indicates that we are in the are below the Background layer/last layer area
+    if (hit.layer < 0)
+      hit.veryBottom = true;
+
     if (hasCapture()) {
       hit.layer = MID(firstLayer(), hit.layer, lastLayer());
       if (isMovingCel())
@@ -1986,8 +2225,8 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
         hit.frame = MID(firstFrame(), hit.frame, lastFrame());
     }
     else {
-      if (hit.layer > lastLayer()) hit.layer = LayerIndex::NoLayer;
-      if (hit.frame > lastFrame()) hit.frame = frame_t(-1);
+      if (hit.layer > lastLayer()) hit.layer = -1;
+      if (hit.frame > lastFrame()) hit.frame = -1;
     }
 
     // Is the mouse over onionskin handles?
@@ -2006,7 +2245,7 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
     // Is the mouse on the frame tags area?
     else if (getPartBounds(Hit(PART_HEADER_FRAME_TAGS)).contains(mousePos)) {
       for (FrameTag* frameTag : m_sprite->frameTags()) {
-        gfx::Rect bounds = getPartBounds(Hit(PART_FRAME_TAG, LayerIndex(0), 0, frameTag->id()));
+        gfx::Rect bounds = getPartBounds(Hit(PART_FRAME_TAG, 0, 0, frameTag->id()));
         if (bounds.contains(mousePos)) {
           hit.part = PART_FRAME_TAG;
           hit.frameTag = frameTag->id();
@@ -2079,18 +2318,14 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
 
 Timeline::Hit Timeline::hitTestCel(const gfx::Point& mousePos)
 {
-  Hit hit(
-    PART_NOTHING,
-    LayerIndex::NoLayer,
-    frame_t(-1));
-
+  Hit hit(PART_NOTHING, -1, -1);
   if (!m_document)
     return hit;
 
   gfx::Point scroll = viewScroll();
   int top = topHeight();
 
-  hit.layer = lastLayer() - LayerIndex(
+  hit.layer = lastLayer() - (
     (mousePos.y
      - top
      - HDRSIZE
@@ -2147,32 +2382,47 @@ void Timeline::updateStatusBar(ui::Message* msg)
       case Range::kFrames:
         if (validFrame(m_hot.frame)) {
           if (m_dropTarget.hhit == DropTarget::Before) {
-            sb->setStatusText(0, "%s before frame %d", verb, int(m_dropRange.frameBegin()+1));
+            sb->setStatusText(0, "%s before frame %d", verb, int(m_dropRange.firstFrame()+1));
             return;
           }
           else if (m_dropTarget.hhit == DropTarget::After) {
-            sb->setStatusText(0, "%s after frame %d", verb, int(m_dropRange.frameEnd()+1));
+            sb->setStatusText(0, "%s after frame %d", verb, int(m_dropRange.lastFrame()+1));
             return;
           }
         }
         break;
 
       case Range::kLayers: {
-        int layerIdx = -1;
-        if (m_dropTarget.vhit == DropTarget::Bottom)
-          layerIdx = m_dropRange.layerBegin();
-        else if (m_dropTarget.vhit == DropTarget::Top)
-          layerIdx = m_dropRange.layerEnd();
+        layer_t firstLayer;
+        layer_t lastLayer;
+        if (!selectedLayersBounds(m_dropRange.selectedLayers(),
+                                  &firstLayer, &lastLayer))
+          break;
 
-        Layer* layer = ((layerIdx >= 0 && layerIdx < (int)m_layers.size()) ? m_layers[layerIdx]: NULL);
+        if (m_dropTarget.vhit == DropTarget::VeryBottom) {
+          sb->setStatusText(0, "%s at the very bottom", verb);
+          return;
+        }
+
+        layer_t layerIdx = -1;
+        if (m_dropTarget.vhit == DropTarget::Bottom ||
+            m_dropTarget.vhit == DropTarget::FirstChild)
+          layerIdx = firstLayer;
+        else if (m_dropTarget.vhit == DropTarget::Top)
+          layerIdx = lastLayer;
+
+        Layer* layer = (validLayer(layerIdx) ? m_layers[layerIdx].layer: nullptr);
         if (layer) {
-          if (m_dropTarget.vhit == DropTarget::Bottom) {
-            sb->setStatusText(0, "%s at bottom of layer %s", verb, layer->name().c_str());
-            return;
-          }
-          else if (m_dropTarget.vhit == DropTarget::Top) {
-            sb->setStatusText(0, "%s at top of layer %s", verb, layer->name().c_str());
-            return;
+          switch (m_dropTarget.vhit) {
+            case DropTarget::Bottom:
+              sb->setStatusText(0, "%s at bottom of layer %s", verb, layer->name().c_str());
+              return;
+            case DropTarget::Top:
+              sb->setStatusText(0, "%s at top of layer %s", verb, layer->name().c_str());
+              return;
+            case DropTarget::FirstChild:
+              sb->setStatusText(0, "%s as first child of layer %s", verb, layer->name().c_str());
+              return;
           }
         }
         break;
@@ -2181,7 +2431,8 @@ void Timeline::updateStatusBar(ui::Message* msg)
     }
   }
   else {
-    Layer* layer = (validLayer(m_hot.layer) ? m_layers[m_hot.layer]: NULL);
+    Layer* layer = (validLayer(m_hot.layer) ? m_layers[m_hot.layer].layer:
+                                              nullptr);
 
     switch (m_hot.part) {
 
@@ -2220,11 +2471,14 @@ void Timeline::updateStatusBar(ui::Message* msg)
         break;
 
       case PART_LAYER_CONTINUOUS_ICON:
-        if (layer != NULL) {
-          sb->setStatusText(0, "Layer '%s' is %s (%s)",
-            layer->name().c_str(),
-            layer->isContinuous() ? "continuous": "discontinuous",
-            layer->isContinuous() ? "prefer linked cels/frames": "prefer individual cels/frames");
+        if (layer) {
+          if (layer->isImage())
+            sb->setStatusText(0, "Layer '%s' is %s (%s)",
+                              layer->name().c_str(),
+                              layer->isContinuous() ? "continuous": "discontinuous",
+                              layer->isContinuous() ? "prefer linked cels/frames": "prefer individual cels/frames");
+          else if (layer->isGroup())
+            sb->setStatusText(0, "Group '%s'", layer->name().c_str());
           return;
         }
         break;
@@ -2262,7 +2516,7 @@ void Timeline::updateStatusBar(ui::Message* msg)
   sb->clearText();
 }
 
-void Timeline::showCel(LayerIndex layer, frame_t frame)
+void Timeline::showCel(layer_t layer, frame_t frame)
 {
   gfx::Point scroll = viewScroll();
 
@@ -2300,7 +2554,7 @@ void Timeline::showCel(LayerIndex layer, frame_t frame)
 
 void Timeline::showCurrentCel()
 {
-  LayerIndex layer = getLayerIndex(m_layer);
+  layer_t layer = getLayerIndex(m_layer);
   if (layer >= firstLayer())
     showCel(layer, m_frame);
 }
@@ -2338,8 +2592,8 @@ gfx::Point Timeline::getMaxScrollablePos() const
 
 bool Timeline::allLayersVisible()
 {
-  for (size_t i=0; i<m_layers.size(); i++)
-    if (!m_layers[i]->isVisible())
+  for (Layer* topLayer : m_sprite->root()->layers())
+    if (!topLayer->isVisible())
       return false;
 
   return true;
@@ -2347,8 +2601,8 @@ bool Timeline::allLayersVisible()
 
 bool Timeline::allLayersInvisible()
 {
-  for (size_t i=0; i<m_layers.size(); i++)
-    if (m_layers[i]->isVisible())
+  for (Layer* topLayer : m_sprite->root()->layers())
+    if (topLayer->isVisible())
       return false;
 
   return true;
@@ -2356,8 +2610,8 @@ bool Timeline::allLayersInvisible()
 
 bool Timeline::allLayersLocked()
 {
-  for (size_t i=0; i<m_layers.size(); i++)
-    if (m_layers[i]->isEditable())
+  for (Layer* topLayer : m_sprite->root()->layers())
+    if (topLayer->isEditable())
       return false;
 
   return true;
@@ -2365,8 +2619,8 @@ bool Timeline::allLayersLocked()
 
 bool Timeline::allLayersUnlocked()
 {
-  for (size_t i=0; i<m_layers.size(); i++)
-    if (!m_layers[i]->isEditable())
+  for (Layer* topLayer : m_sprite->root()->layers())
+    if (!topLayer->isEditable())
       return false;
 
   return true;
@@ -2375,7 +2629,7 @@ bool Timeline::allLayersUnlocked()
 bool Timeline::allLayersContinuous()
 {
   for (size_t i=0; i<m_layers.size(); i++)
-    if (!m_layers[i]->isContinuous())
+    if (!m_layers[i].layer->isContinuous())
       return false;
 
   return true;
@@ -2384,37 +2638,35 @@ bool Timeline::allLayersContinuous()
 bool Timeline::allLayersDiscontinuous()
 {
   for (size_t i=0; i<m_layers.size(); i++)
-    if (m_layers[i]->isContinuous())
+    if (m_layers[i].layer->isContinuous())
       return false;
 
   return true;
 }
 
-LayerIndex Timeline::getLayerIndex(const Layer* layer) const
+layer_t Timeline::getLayerIndex(const Layer* layer) const
 {
   for (int i=0; i<(int)m_layers.size(); i++)
-    if (m_layers[i] == layer) {
-      ASSERT(m_sprite->layerToIndex(layer) == LayerIndex(i));
-      return LayerIndex(i);
-    }
+    if (m_layers[i].layer == layer)
+      return i;
 
-  return LayerIndex::NoLayer;
+  return -1;
 }
 
-bool Timeline::isLayerActive(LayerIndex layerIndex) const
+bool Timeline::isLayerActive(const layer_t layerIndex) const
 {
   if (layerIndex == getLayerIndex(m_layer))
     return true;
   else
-    return m_range.inRange(layerIndex);
+    return m_range.contains(m_layers[layerIndex].layer);
 }
 
-bool Timeline::isFrameActive(frame_t frame) const
+bool Timeline::isFrameActive(const frame_t frame) const
 {
   if (frame == m_frame)
     return true;
   else
-    return m_range.inRange(frame);
+    return m_range.contains(frame);
 }
 
 void Timeline::dropRange(DropOp op)
@@ -2422,15 +2674,33 @@ void Timeline::dropRange(DropOp op)
   bool copy = (op == Timeline::kCopy);
   Range newFromRange;
   DocumentRangePlace place = kDocumentRangeAfter;
+  Range dropRange = m_dropRange;
 
   switch (m_range.type()) {
+
     case Range::kFrames:
       if (m_dropTarget.hhit == DropTarget::Before)
         place = kDocumentRangeBefore;
       break;
+
     case Range::kLayers:
-      if (m_dropTarget.vhit == DropTarget::Bottom)
-        place = kDocumentRangeBefore;
+      switch (m_dropTarget.vhit) {
+        case DropTarget::Bottom:
+          place = kDocumentRangeBefore;
+          break;
+        case DropTarget::FirstChild:
+          place = kDocumentRangeFirstChild;
+          break;
+        case DropTarget::VeryBottom:
+          place = kDocumentRangeBefore;
+          {
+            Layer* layer = m_sprite->root()->firstLayer();
+            dropRange.clearRange();
+            dropRange.startRange(layer, -1, Range::kLayers);
+            dropRange.endRange(layer, -1);
+          }
+          break;
+      }
       break;
   }
 
@@ -2438,9 +2708,9 @@ void Timeline::dropRange(DropOp op)
 
   try {
     if (copy)
-      newFromRange = copy_range(m_document, m_range, m_dropRange, place);
+      newFromRange = copy_range(m_document, m_range, dropRange, place);
     else
-      newFromRange = move_range(m_document, m_range, m_dropRange, place);
+      newFromRange = move_range(m_document, m_range, dropRange, place);
 
     // If we drop a cel in the same frame (but in another layer),
     // document views are not updated, so we are forcing the updating of
@@ -2488,57 +2758,24 @@ void Timeline::updateDropRange(const gfx::Point& pt)
   m_dropTarget.vhit = DropTarget::VNone;
 
   if (m_state != STATE_MOVING_RANGE) {
-    m_dropRange.disableRange();
+    m_dropRange.clearRange();
     return;
   }
 
   switch (m_range.type()) {
 
-    case Range::kCels: {
-      frame_t dx = m_hot.frame - m_clk.frame;
-      LayerIndex dy = m_hot.layer - m_clk.layer;
-
-      LayerIndex layerIdx = dy+m_range.layerBegin();
-      layerIdx = MID(firstLayer(), layerIdx, LayerIndex(m_layers.size() - m_range.layers()));
-
-      frame_t frame = dx+m_range.frameBegin();
-      frame = MAX(firstFrame(), frame);
-
-      m_dropRange.startRange(layerIdx, frame, m_range.type());
-      m_dropRange.endRange(
-        layerIdx+LayerIndex(m_range.layers()-1),
-        frame+m_range.frames()-1);
+    case Range::kCels:
+      m_dropRange = m_range;
+      m_dropRange.displace(m_hot.layer - m_clk.layer,
+                           m_hot.frame - m_clk.frame);
       break;
-    }
 
-    case Range::kFrames: {
-      frame_t frame = m_hot.frame;
-      frame_t frameEnd = frame;
-
-      if (frame >= m_range.frameBegin() && frame <= m_range.frameEnd()) {
-        frame = m_range.frameBegin();
-        frameEnd = frame + m_range.frames() - 1;
-      }
-
-      LayerIndex layerIdx = getLayerIndex(m_layer);
-      m_dropRange.startRange(layerIdx, frame, m_range.type());
-      m_dropRange.endRange(layerIdx, frameEnd);
+    case Range::kFrames:
+    case Range::kLayers:
+      m_dropRange.clearRange();
+      m_dropRange.startRange(m_layers[m_hot.layer].layer, m_hot.frame, m_range.type());
+      m_dropRange.endRange(m_layers[m_hot.layer].layer, m_hot.frame);
       break;
-    }
-
-    case Range::kLayers: {
-      LayerIndex layer = m_hot.layer;
-      LayerIndex layerEnd = layer;
-
-      if (layer >= m_range.layerBegin() && layer <= m_range.layerEnd()) {
-        layer = m_range.layerBegin();
-        layerEnd = layer + LayerIndex(m_range.layers() - 1);
-      }
-
-      m_dropRange.startRange(layer, m_frame, m_range.type());
-      m_dropRange.endRange(layerEnd, m_frame);
-      break;
-    }
   }
 
   gfx::Rect bounds = getRangeBounds(m_dropRange);
@@ -2548,10 +2785,21 @@ void Timeline::updateDropRange(const gfx::Point& pt)
   else
     m_dropTarget.hhit = DropTarget::After;
 
-  if (pt.y < bounds.y + bounds.h/2)
+  if (m_hot.veryBottom)
+    m_dropTarget.vhit = DropTarget::VeryBottom;
+  else if (pt.y < bounds.y + bounds.h/2)
     m_dropTarget.vhit = DropTarget::Top;
-  else
+  // Special drop target for expanded groups
+  else if (m_range.type() == Range::kLayers &&
+           m_hot.layer >= 0 &&
+           m_hot.layer < m_layers.size() &&
+           m_layers[m_hot.layer].layer->isGroup() &&
+           static_cast<LayerGroup*>(m_layers[m_hot.layer].layer)->isExpanded()) {
+    m_dropTarget.vhit = DropTarget::FirstChild;
+  }
+  else {
     m_dropTarget.vhit = DropTarget::Bottom;
+  }
 
   if (oldHHit != m_dropTarget.hhit ||
       oldVHit != m_dropTarget.vhit) {
@@ -2618,7 +2866,7 @@ void Timeline::onNewInputPriority(InputChainElement* element)
   // That is why we don't disable the range in this case.
   Workspace* workspace = dynamic_cast<Workspace*>(element);
   if (!workspace) {
-    m_range.disableRange();
+    m_range.clearRange();
     invalidate();
   }
 }
@@ -2703,7 +2951,7 @@ bool Timeline::onClear(Context* ctx)
 
 void Timeline::onCancel(Context* ctx)
 {
-  m_range.disableRange();
+  m_range.clearRange();
   clearClipboardRange();
   invalidate();
 }
diff --git a/src/app/ui/timeline.h b/src/app/ui/timeline.h
index 2a72342e4..7cdc196b7 100644
--- a/src/app/ui/timeline.h
+++ b/src/app/ui/timeline.h
@@ -18,7 +18,8 @@
 #include "doc/document_observer.h"
 #include "doc/documents_observer.h"
 #include "doc/frame.h"
-#include "doc/layer_index.h"
+#include "doc/selected_frames.h"
+#include "doc/selected_layers.h"
 #include "doc/sprite.h"
 #include "ui/scroll_bar.h"
 #include "ui/timer.h"
@@ -88,6 +89,8 @@ namespace app {
     bool isMovingCel() const;
 
     Range range() const { return m_range; }
+    const SelectedLayers& selectedLayers() const { return m_range.selectedLayers(); }
+    const SelectedFrames& selectedFrames() const { return m_range.selectedFrames(); }
 
     void prepareToMoveRange();
     void moveRange(Range& range);
@@ -147,12 +150,13 @@ namespace app {
 
     struct Hit {
       int part;
-      LayerIndex layer;
+      layer_t layer;
       frame_t frame;
       ObjectId frameTag;
+      bool veryBottom;
 
-      Hit(int part = 0, LayerIndex layer = LayerIndex(0), frame_t frame = 0, ObjectId frameTag = NullId)
-        : part(part), layer(layer), frame(frame), frameTag(frameTag) {
+      Hit(int part = 0, layer_t layer = -1, frame_t frame = 0, ObjectId frameTag = NullId)
+        : part(part), layer(layer), frame(frame), frameTag(frameTag), veryBottom(false) {
       }
 
       bool operator!=(const Hit& other) const {
@@ -167,8 +171,20 @@ namespace app {
     };
 
     struct DropTarget {
-      enum HHit { HNone, Before, After };
-      enum VHit { VNone, Bottom, Top };
+
+      enum HHit {
+        HNone,
+        Before,
+        After
+      };
+
+      enum VHit {
+        VNone,
+        Bottom,
+        Top,
+        FirstChild,
+        VeryBottom
+      };
 
       DropTarget() {
         hhit = HNone;
@@ -178,11 +194,40 @@ namespace app {
       HHit hhit;
       VHit vhit;
       Layer* layer;
-      LayerIndex layerIdx;
+      ObjectId layerId;
       frame_t frame;
       int xpos, ypos;
     };
 
+    struct LayerInfo {
+      Layer* layer;
+      int level;
+      LayerFlags inheritedFlags;
+
+      LayerInfo()
+        : layer(nullptr),
+          level(0),
+          inheritedFlags(LayerFlags::None) {
+      }
+
+      LayerInfo(Layer* layer, int level, LayerFlags inheritedFlags)
+        : layer(layer),
+          level(level),
+          inheritedFlags(inheritedFlags) {
+      }
+
+      bool parentVisible() const {
+        return ((int(inheritedFlags) & int(LayerFlags::Visible)) != 0);
+      }
+
+      bool parentEditable() const {
+        return ((int(inheritedFlags) & int(LayerFlags::Editable)) != 0);
+      }
+    };
+
+    bool selectedLayersBounds(const SelectedLayers& layers,
+                              layer_t* first, layer_t* last) const;
+
     void setLayer(Layer* layer);
     void setFrame(frame_t frame, bool byUser);
     bool allLayersVisible();
@@ -193,23 +238,24 @@ namespace app {
     bool allLayersDiscontinuous();
     void detachDocument();
     void setCursor(ui::Message* msg, const Hit& hit);
-    void getDrawableLayers(ui::Graphics* g, LayerIndex* first_layer, LayerIndex* last_layer);
-    void getDrawableFrames(ui::Graphics* g, frame_t* first_frame, frame_t* last_frame);
+    void getDrawableLayers(ui::Graphics* g, layer_t* firstLayer, layer_t* lastLayer);
+    void getDrawableFrames(ui::Graphics* g, frame_t* firstFrame, frame_t* lastFrame);
     void drawPart(ui::Graphics* g, const gfx::Rect& bounds,
-      const char* text, skin::Style* style,
-      bool is_active = false, bool is_hover = false, bool is_clicked = false);
+                  const char* text, skin::Style* style,
+                  bool is_active = false, bool is_hover = false,
+                  bool is_clicked = false, bool is_disabled = false);
     void drawTop(ui::Graphics* g);
     void drawHeader(ui::Graphics* g);
     void drawHeaderFrame(ui::Graphics* g, frame_t frame);
-    void drawLayer(ui::Graphics* g, LayerIndex layerIdx);
-    void drawCel(ui::Graphics* g, LayerIndex layerIdx, frame_t frame, Cel* cel, DrawCelData* data);
+    void drawLayer(ui::Graphics* g, layer_t layerIdx);
+    void drawCel(ui::Graphics* g, layer_t layerIdx, frame_t frame, Cel* cel, DrawCelData* data);
     void drawCelLinkDecorators(ui::Graphics* g, const gfx::Rect& bounds,
                                Cel* cel, frame_t frame, bool is_active, bool is_hover,
                                DrawCelData* data);
     void drawFrameTags(ui::Graphics* g);
     void drawRangeOutline(ui::Graphics* g);
     void drawPaddings(ui::Graphics* g);
-    bool drawPart(ui::Graphics* g, int part, LayerIndex layer, frame_t frame);
+    bool drawPart(ui::Graphics* g, int part, layer_t layer, frame_t frame);
     void drawClipboardRange(ui::Graphics* g);
     gfx::Rect getLayerHeadersBounds() const;
     gfx::Rect getFrameHeadersBounds() const;
@@ -224,14 +270,14 @@ namespace app {
     Hit hitTest(ui::Message* msg, const gfx::Point& mousePos);
     Hit hitTestCel(const gfx::Point& mousePos);
     void setHot(const Hit& hit);
-    void showCel(LayerIndex layer, frame_t frame);
+    void showCel(layer_t layer, frame_t frame);
     void showCurrentCel();
     void cleanClk();
     gfx::Size getScrollableSize() const;
     gfx::Point getMaxScrollablePos() const;
-    LayerIndex getLayerIndex(const Layer* layer) const;
-    bool isLayerActive(LayerIndex layerIdx) const;
-    bool isFrameActive(frame_t frame) const;
+    layer_t getLayerIndex(const Layer* layer) const;
+    bool isLayerActive(const layer_t layerIdx) const;
+    bool isFrameActive(const frame_t frame) const;
     void updateStatusBar(ui::Message* msg);
     void updateDropRange(const gfx::Point& pt);
     void clearClipboardRange();
@@ -239,15 +285,14 @@ namespace app {
     bool isCopyKeyPressed(ui::Message* msg);
 
     // The layer of the bottom (e.g. Background layer)
-    LayerIndex firstLayer() const { return LayerIndex(0); }
-
+    layer_t firstLayer() const { return 0; }
     // The layer of the top.
-    LayerIndex lastLayer() const { return LayerIndex(m_layers.size()-1); }
+    layer_t lastLayer() const { return m_layers.size()-1; }
 
     frame_t firstFrame() const { return frame_t(0); }
     frame_t lastFrame() const { return m_sprite->lastFrame(); }
 
-    bool validLayer(LayerIndex layer) const { return layer >= firstLayer() && layer <= lastLayer(); }
+    bool validLayer(layer_t layer) const { return layer >= firstLayer() && layer <= lastLayer(); }
     bool validFrame(frame_t frame) const { return frame >= firstFrame() && frame <= lastFrame(); }
 
     int topHeight() const;
@@ -265,9 +310,10 @@ namespace app {
     Layer* m_layer;
     frame_t m_frame;
     Range m_range;
+    Range m_startRange;
     Range m_dropRange;
     State m_state;
-    std::vector<Layer*> m_layers;
+    std::vector<LayerInfo> m_layers;
     int m_separator_x;
     int m_separator_w;
     int m_origFrames;
@@ -293,7 +339,7 @@ namespace app {
 
     // Temporal data used to move the range.
     struct MoveRange {
-      int activeRelativeLayer;
+      layer_t activeRelativeLayer;
       frame_t activeRelativeFrame;
     } m_moveRangeData;
   };
diff --git a/src/app/ui_context.cpp b/src/app/ui_context.cpp
index 88fedebef..5407dac4b 100644
--- a/src/app/ui_context.cpp
+++ b/src/app/ui_context.cpp
@@ -221,13 +221,38 @@ void UIContext::onGetActiveSite(Site* site) const
   DocumentView* view = activeView();
   if (view) {
     view->getSite(site);
+
+    if (site->sprite()) {
+      // Selected layers
+      Timeline* timeline = App::instance()->timeline();
+      if (timeline &&
+          timeline->range().enabled()) {
+        switch (timeline->range().type()) {
+          case DocumentRange::kCels:   site->focus(Site::InCels); break;
+          case DocumentRange::kFrames: site->focus(Site::InFrames); break;
+          case DocumentRange::kLayers: site->focus(Site::InLayers); break;
+        }
+        site->selectedLayers(timeline->selectedLayers());
+        site->selectedFrames(timeline->selectedFrames());
+      }
+      else {
+        ColorBar* colorBar = ColorBar::instance();
+        if (colorBar &&
+            colorBar->getPaletteView()->getSelectedEntriesCount() > 0) {
+          site->focus(Site::InColorBar);
+        }
+        else {
+          site->focus(Site::InEditor);
+        }
+      }
+    }
   }
   // Default/dummy site (maybe for batch/command line mode)
   else if (!isUIAvailable()) {
     if (Document* doc = m_lastSelectedDoc) {
       site->document(doc);
       site->sprite(doc->sprite());
-      site->layer(doc->sprite()->indexToLayer(LayerIndex(0)));
+      site->layer(doc->sprite()->root()->firstLayer());
       site->frame(0);
     }
   }
diff --git a/src/app/util/clipboard.cpp b/src/app/util/clipboard.cpp
index 7e80afe9e..181888da0 100644
--- a/src/app/util/clipboard.cpp
+++ b/src/app/util/clipboard.cpp
@@ -348,33 +348,28 @@ void paste()
       DocumentRange srcRange = clipboard_range.range();
       Document* srcDoc = clipboard_range.document();
       Sprite* srcSpr = srcDoc->sprite();
-      std::vector<Layer*> srcLayers;
-      std::vector<Layer*> dstLayers;
-      srcSpr->getLayersList(srcLayers);
-      dstSpr->getLayersList(dstLayers);
 
       switch (srcRange.type()) {
 
         case DocumentRange::kCels: {
+          Layer* dstLayer = editor->layer();
+          frame_t dstFrameFirst = editor->frame();
+
+          DocumentRange dstRange;
+          dstRange.startRange(dstLayer, dstFrameFirst, DocumentRange::kCels);
+          for (layer_t i=1; i<srcRange.layers(); ++i) {
+            dstLayer = dstLayer->getPreviousInWholeHierarchy();
+            if (dstLayer == nullptr)
+              break;
+          }
+          dstRange.endRange(dstLayer, dstFrameFirst+srcRange.frames()-1);
+
           // We can use a document range op (copy_range) to copy/paste
           // cels in the same document.
           if (srcDoc == dstDoc) {
-            Timeline* timeline = App::instance()->timeline();
-            DocumentRange dstRange = timeline->range();
-            LayerIndex dstLayer = srcSpr->layerToIndex(editor->layer());
-            frame_t dstFrame = editor->frame();
-
-            if (dstRange.enabled()) {
-              dstLayer = dstRange.layerEnd();
-              dstFrame = dstRange.frameBegin();
-            }
-
-            LayerIndex dstLayer2(int(dstLayer)-srcRange.layers()+1);
-            dstRange.startRange(dstLayer, dstFrame, DocumentRange::kCels);
-            dstRange.endRange(dstLayer2, dstFrame+srcRange.frames()-1);
-
             // This is the app::copy_range (not clipboard::copy_range()).
-            app::copy_range(srcDoc, srcRange, dstRange, kDocumentRangeBefore);
+            if (srcRange.layers() == dstRange.layers())
+              app::copy_range(srcDoc, srcRange, dstRange, kDocumentRangeBefore);
             editor->invalidate();
             return;
           }
@@ -383,32 +378,36 @@ void paste()
           DocumentApi api = dstDoc->getApi(transaction);
 
           // Add extra frames if needed
-          frame_t dstFrameBegin = editor->frame();
-          while (dstFrameBegin+srcRange.frames() > dstSpr->totalFrames())
+          while (dstFrameFirst+srcRange.frames() > dstSpr->totalFrames())
             api.addFrame(dstSpr, dstSpr->totalFrames());
 
-          for (LayerIndex
-                 i = srcRange.layerEnd(),
-                 j = dstSpr->layerToIndex(editor->layer());
-               i >= srcRange.layerBegin() &&
-                 i >= LayerIndex(0) &&
-                 j >= LayerIndex(0); --i, --j) {
+          auto srcIt = srcRange.selectedLayers().begin();
+          auto dstIt = dstRange.selectedLayers().begin();
+          auto srcEnd = srcRange.selectedLayers().end();
+          auto dstEnd = dstRange.selectedLayers().end();
+
+          for (; srcIt != srcEnd && dstIt != dstEnd; ++srcIt, ++dstIt) {
+            auto srcLayer = *srcIt;
+            auto dstLayer = *dstIt;
+
+            if (!srcLayer->isImage() ||
+                !dstLayer->isImage())
+              continue;
+
             // Maps a linked Cel in the original sprite with its
             // corresponding copy in the new sprite. In this way
             // we can.
             std::map<Cel*, Cel*> relatedCels;
 
-            for (frame_t frame = srcRange.frameBegin(),
-                   dstFrame = dstFrameBegin;
-                 frame <= srcRange.frameEnd();
-                 ++frame, ++dstFrame) {
-              Cel* srcCel = srcLayers[i]->cel(frame);
+            frame_t dstFrame = dstFrameFirst;
+            for (frame_t srcFrame : srcRange.selectedFrames()) {
+              Cel* srcCel = srcLayer->cel(srcFrame);
               Cel* srcLink = nullptr;
 
               if (srcCel && srcCel->image()) {
                 bool createCopy = true;
 
-                if (dstLayers[j]->isContinuous() &&
+                if (dstLayer->isContinuous() &&
                     srcCel->links()) {
                   srcLink = srcCel->link();
                   if (!srcLink)
@@ -421,28 +420,29 @@ void paste()
 
                       // Create a link from dstRelated
                       api.copyCel(
-                        static_cast<LayerImage*>(dstLayers[j]), dstRelated->frame(),
-                        static_cast<LayerImage*>(dstLayers[j]), dstFrame);
+                        static_cast<LayerImage*>(dstLayer), dstRelated->frame(),
+                        static_cast<LayerImage*>(dstLayer), dstFrame);
                     }
                   }
                 }
 
                 if (createCopy) {
                   api.copyCel(
-                    static_cast<LayerImage*>(srcLayers[i]), frame,
-                    static_cast<LayerImage*>(dstLayers[j]), dstFrame);
+                    static_cast<LayerImage*>(srcLayer), srcFrame,
+                    static_cast<LayerImage*>(dstLayer), dstFrame);
 
                   if (srcLink)
-                    relatedCels[srcLink] = dstLayers[j]->cel(dstFrame);
+                    relatedCels[srcLink] = dstLayer->cel(dstFrame);
                 }
               }
               else {
-                Cel* dstCel = dstLayers[j]->cel(dstFrame);
+                Cel* dstCel = dstLayer->cel(dstFrame);
                 if (dstCel)
                   api.clearCel(dstCel);
               }
-            }
 
+              ++dstFrame;
+            }
           }
 
           transaction.commit();
@@ -451,42 +451,49 @@ void paste()
         }
 
         case DocumentRange::kFrames: {
-          Transaction transaction(UIContext::instance(), "Paste Frames");
-          DocumentApi api = dstDoc->getApi(transaction);
           frame_t dstFrame = editor->frame();
 
+          // We use a DocumentRange operation to copy frames inside
+          // the same sprite.
           if (srcSpr == dstSpr) {
-            if (srcRange.inRange(dstFrame))
-              dstFrame = srcRange.frameEnd()+1;
+            DocumentRange dstRange;
+            dstRange.startRange(nullptr, dstFrame, DocumentRange::kFrames);
+            dstRange.endRange(nullptr, dstFrame);
+            app::copy_range(srcDoc, srcRange, dstRange, kDocumentRangeBefore);
+            break;
           }
 
-          frame_t srcFrame = srcRange.frameBegin();
-          for (frame_t frame = srcRange.frameBegin(); frame <= srcRange.frameEnd(); ++frame) {
+          Transaction transaction(UIContext::instance(), "Paste Frames");
+          DocumentApi api = dstDoc->getApi(transaction);
+
+          auto srcLayers = srcSpr->allBrowsableLayers();
+          auto dstLayers = dstSpr->allBrowsableLayers();
+
+          for (frame_t srcFrame : srcRange.selectedFrames()) {
             api.addEmptyFrame(dstSpr, dstFrame);
-
-            // If we are copying frames from/to the same sprite, we
-            // have to adjust the source frame.
-            if (srcSpr == dstSpr) {
-              if (dstFrame < srcFrame)
-                ++srcFrame;
-            }
-
             api.setFrameDuration(dstSpr, dstFrame, srcSpr->frameDuration(srcFrame));
 
-            for (LayerIndex
-                   i = LayerIndex(srcLayers.size()-1),
-                   j = LayerIndex(dstLayers.size()-1);
-                   i >= LayerIndex(0) &&
-                   j >= LayerIndex(0); --i, --j) {
-              Cel* cel = static_cast<LayerImage*>(srcLayers[i])->cel(srcFrame);
+            auto srcIt = srcLayers.begin();
+            auto dstIt = dstLayers.begin();
+            auto srcEnd = srcLayers.end();
+            auto dstEnd = dstLayers.end();
+
+            for (; srcIt != srcEnd && dstIt != dstEnd; ++srcIt, ++dstIt) {
+              auto srcLayer = *srcIt;
+              auto dstLayer = *dstIt;
+
+              if (!srcLayer->isImage() ||
+                  !dstLayer->isImage())
+                continue;
+
+              Cel* cel = static_cast<LayerImage*>(srcLayer)->cel(srcFrame);
               if (cel && cel->image()) {
                 api.copyCel(
-                  static_cast<LayerImage*>(srcLayers[i]), srcFrame,
-                  static_cast<LayerImage*>(dstLayers[j]), dstFrame);
+                  static_cast<LayerImage*>(srcLayer), srcFrame,
+                  static_cast<LayerImage*>(dstLayer), dstFrame);
               }
             }
 
-            ++srcFrame;
             ++dstFrame;
           }
 
@@ -502,39 +509,49 @@ void paste()
           Transaction transaction(UIContext::instance(), "Paste Layers");
           DocumentApi api = dstDoc->getApi(transaction);
 
+          // Remove children if their parent is selected so we only
+          // copy the parent.
+          SelectedLayers srcLayersSet = srcRange.selectedLayers();
+          srcLayersSet.removeChildrenIfParentIsSelected();
+          LayerList srcLayers = srcLayersSet.toLayerList();
+
           // Expand frames of dstDoc if it's needed.
-          frame_t maxFrame(0);
-          for (LayerIndex i = srcRange.layerBegin();
-               i <= srcRange.layerEnd() &&
-               i < LayerIndex(srcLayers.size()); ++i) {
-            Cel* lastCel = static_cast<LayerImage*>(srcLayers[i])->getLastCel();
+          frame_t maxFrame = 0;
+          for (Layer* srcLayer : srcLayers) {
+            if (!srcLayer->isImage())
+              continue;
+
+            Cel* lastCel = static_cast<LayerImage*>(srcLayer)->getLastCel();
             if (lastCel && maxFrame < lastCel->frame())
               maxFrame = lastCel->frame();
           }
           while (dstSpr->totalFrames() < maxFrame+1)
             api.addEmptyFrame(dstSpr, dstSpr->totalFrames());
 
-          for (LayerIndex i = srcRange.layerBegin(); i <= srcRange.layerEnd(); ++i) {
+          for (Layer* srcLayer : srcLayers) {
             Layer* afterThis;
-            if (srcLayers[i]->isBackground() &&
-                !dstDoc->sprite()->backgroundLayer()) {
+            if (srcLayer->isBackground() && !dstDoc->sprite()->backgroundLayer())
               afterThis = nullptr;
-            }
             else
-              afterThis = dstSpr->folder()->getLastLayer();
+              afterThis = dstSpr->root()->lastLayer();
 
-            LayerImage* newLayer = new LayerImage(dstSpr);
-            api.addLayer(dstSpr->folder(), newLayer, afterThis);
+            Layer* newLayer = nullptr;
+            if (srcLayer->isImage())
+              newLayer = new LayerImage(dstSpr);
+            else if (srcLayer->isGroup())
+              newLayer = new LayerGroup(dstSpr);
+            else
+              continue;
 
-            srcDoc->copyLayerContent(
-              srcLayers[i], dstDoc, newLayer);
+            api.addLayer(dstSpr->root(), newLayer, afterThis);
+
+            srcDoc->copyLayerContent(srcLayer, dstDoc, newLayer);
           }
 
           transaction.commit();
           editor->invalidate();
           break;
         }
-
       }
       break;
     }
diff --git a/src/app/util/range_utils.cpp b/src/app/util/range_utils.cpp
index 3ddab85aa..5475bbe7d 100644
--- a/src/app/util/range_utils.cpp
+++ b/src/app/util/range_utils.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2001-2015  David Capello
+// Copyright (C) 2001-2016  David Capello
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License version 2 as
@@ -34,16 +34,12 @@ CelList get_unique_cels(Sprite* sprite, const DocumentRange& inrange)
 
   std::set<ObjectId> visited;
 
-  for (LayerIndex layerIdx = range.layerBegin(); layerIdx <= range.layerEnd(); ++layerIdx) {
-    Layer* layer = sprite->indexToLayer(layerIdx);
+  for (Layer* layer : range.selectedLayers()) {
     if (!layer || !layer->isImage())
       continue;
 
     LayerImage* layerImage = static_cast<LayerImage*>(layer);
-    for (frame_t frame = range.frameEnd(),
-           begin = range.frameBegin()-1;
-         frame != begin;
-         --frame) {
+    for (frame_t frame : range.selectedFrames()) {
       Cel* cel = layerImage->cel(frame);
       if (!cel)
         continue;
diff --git a/src/doc/CMakeLists.txt b/src/doc/CMakeLists.txt
index e43f6dafb..6985030a2 100644
--- a/src/doc/CMakeLists.txt
+++ b/src/doc/CMakeLists.txt
@@ -42,9 +42,8 @@ add_library(doc-lib
   image_io.cpp
   images_collector.cpp
   layer.cpp
-  layer_index.cpp
   layer_io.cpp
-  layers_range.cpp
+  layer_list.cpp
   mask.cpp
   mask_boundaries.cpp
   mask_io.cpp
@@ -55,6 +54,8 @@ add_library(doc-lib
   primitives.cpp
   remap.cpp
   rgbmap.cpp
+  selected_frames.cpp
+  selected_layers.cpp
   site.cpp
   sort_palette.cpp
   sprite.cpp
diff --git a/src/doc/LICENSE.txt b/src/doc/LICENSE.txt
index 7ed8f201a..0d2d81fd4 100644
--- a/src/doc/LICENSE.txt
+++ b/src/doc/LICENSE.txt
@@ -1,4 +1,4 @@
-Copyright (c) 2001-2015 David Capello
+Copyright (c) 2001-2016 David Capello
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
diff --git a/src/doc/README.md b/src/doc/README.md
index e32066553..6c5409397 100644
--- a/src/doc/README.md
+++ b/src/doc/README.md
@@ -1,4 +1,4 @@
 # Aseprite Document Library
-*Copyright (C) 2001-2015 David Capello*
+*Copyright (C) 2001-2016 David Capello*
 
 > Distributed under [MIT license](LICENSE.txt)
diff --git a/src/doc/cels_range.cpp b/src/doc/cels_range.cpp
index 403812ced..79582fbfc 100644
--- a/src/doc/cels_range.cpp
+++ b/src/doc/cels_range.cpp
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -17,34 +17,46 @@
 namespace doc {
 
 CelsRange::CelsRange(const Sprite* sprite,
-  frame_t first, frame_t last, Flags flags)
-  : m_begin(sprite, first, last, flags)
-  , m_end()
+                     const SelectedFrames& selFrames,
+                     const Flags flags)
+  : m_selFrames(selFrames)
+  , m_begin(sprite, m_selFrames, flags)
+  , m_end(m_selFrames)
 {
 }
 
-CelsRange::iterator::iterator()
+CelsRange::iterator::iterator(const SelectedFrames& selFrames)
   : m_cel(nullptr)
+  , m_selFrames(selFrames)
+  , m_frameIterator(selFrames.begin())
 {
 }
 
-CelsRange::iterator::iterator(const Sprite* sprite, frame_t first, frame_t last, CelsRange::Flags flags)
+CelsRange::iterator::iterator(const Sprite* sprite,
+                              const SelectedFrames& selFrames,
+                              const CelsRange::Flags flags)
   : m_cel(nullptr)
-  , m_first(first)
-  , m_last(last)
+  , m_selFrames(selFrames)
+  , m_frameIterator(selFrames.begin())
   , m_flags(flags)
 {
   // Get first cel
-  Layer* layer = sprite->layer(sprite->firstLayer());
+  Layer* layer = sprite->root()->firstLayer();
   while (layer && !m_cel) {
-    for (frame_t f=first; f<=last; ++f) {
-      m_cel = layer->cel(f);
-      if (m_cel)
-        break;
-      m_cel = nullptr;
+    if (layer->isImage()) {
+      m_frameIterator = m_selFrames.begin();
+      auto endFrame = m_selFrames.end();
+      for (; m_frameIterator!=endFrame; ++m_frameIterator) {
+        m_cel = layer->cel(*m_frameIterator);
+        if (m_cel)
+          break;
+      }
     }
-    layer = layer->getNext();
+
+    if (!m_cel)
+      layer = layer->getNextInWholeHierarchy();
   }
+
   if (m_cel && flags == CelsRange::UNIQUE)
     m_visited.insert(m_cel->data()->id());
 }
@@ -54,29 +66,35 @@ CelsRange::iterator& CelsRange::iterator::operator++()
   if (!m_cel)
     return *this;
 
-  // Get next cel
-  Layer* layer = m_cel->layer();
-  frame_t first = m_cel->frame()+1;
-  m_cel = nullptr;
+  auto endFrame = m_selFrames.end();
+  if (m_frameIterator != endFrame)
+    ++m_frameIterator;
 
+  Layer* layer = m_cel->layer();
+  m_cel = nullptr;
   while (layer && !m_cel) {
-    for (frame_t f=first; f<=m_last; ++f) {
-      m_cel = layer->cel(f);
-      if (m_cel) {
-        if (m_flags == CelsRange::UNIQUE) {
-          if (m_visited.find(m_cel->data()->id()) == m_visited.end()) {
-            m_visited.insert(m_cel->data()->id());
-            break;
+    if (layer->isImage()) {
+      for (; m_frameIterator!=endFrame; ++m_frameIterator) {
+        m_cel = layer->cel(*m_frameIterator);
+        if (m_cel) {
+          if (m_flags == CelsRange::UNIQUE) {
+            if (m_visited.find(m_cel->data()->id()) == m_visited.end()) {
+              m_visited.insert(m_cel->data()->id());
+              break;
+            }
+            else
+              m_cel = nullptr;
           }
           else
-            m_cel = nullptr;
+            break;
         }
-        else
-          break;
       }
     }
-    layer = layer->getNext();
-    first = m_first;
+
+    if (!m_cel) {
+      layer = layer->getNextInWholeHierarchy();
+      m_frameIterator = m_selFrames.begin();
+    }
   }
   return *this;
 }
diff --git a/src/doc/cels_range.h b/src/doc/cels_range.h
index d14e20ba0..ecb057d06 100644
--- a/src/doc/cels_range.h
+++ b/src/doc/cels_range.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -10,11 +10,15 @@
 
 #include "doc/frame.h"
 #include "doc/object_id.h"
+#include "doc/selected_frames.h"
 
 #include <set>
 
 namespace doc {
+
   class Cel;
+  class Layer;
+  class SelectedFrames;
   class Sprite;
 
   class CelsRange {
@@ -25,12 +29,15 @@ namespace doc {
     };
 
     CelsRange(const Sprite* sprite,
-      frame_t first, frame_t last, Flags flags = ALL);
+              const SelectedFrames& selFrames,
+              const Flags flags = ALL);
 
     class iterator {
     public:
-      iterator();
-      iterator(const Sprite* sprite, frame_t first, frame_t last, Flags flags);
+      iterator(const SelectedFrames& selFrames);
+      iterator(const Sprite* sprite,
+               const SelectedFrames& selFrames,
+               const Flags flags);
 
       bool operator==(const iterator& other) const {
         return m_cel == other.m_cel;
@@ -48,7 +55,8 @@ namespace doc {
 
     private:
       Cel* m_cel;
-      frame_t m_first, m_last;
+      const SelectedFrames& m_selFrames;
+      SelectedFrames::const_iterator m_frameIterator;
       Flags m_flags;
       std::set<ObjectId> m_visited;
     };
@@ -57,6 +65,7 @@ namespace doc {
     iterator end() { return m_end; }
 
   private:
+    SelectedFrames m_selFrames;
     iterator m_begin, m_end;
   };
 
diff --git a/src/doc/frame_range.h b/src/doc/frame_range.h
new file mode 100644
index 000000000..ce1b3b935
--- /dev/null
+++ b/src/doc/frame_range.h
@@ -0,0 +1,40 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef DOC_FRAME_RANGE_H_INCLUDED
+#define DOC_FRAME_RANGE_H_INCLUDED
+#pragma once
+
+#include "doc/frame.h"
+
+namespace doc {
+
+  struct FrameRange {
+    frame_t fromFrame, toFrame;
+
+    FrameRange() : fromFrame(0), toFrame(0) {
+    }
+
+    explicit FrameRange(frame_t frame)
+      : fromFrame(frame), toFrame(frame) {
+    }
+
+    FrameRange(frame_t fromFrame, frame_t toFrame)
+      : fromFrame(fromFrame), toFrame(toFrame) {
+    }
+
+    bool operator==(const FrameRange& o) const {
+      return (fromFrame == o.fromFrame && toFrame == o.toFrame);
+    }
+
+    bool operator!=(const FrameRange& o) const {
+      return !operator==(o);
+    }
+  };
+
+} // namespace doc
+
+#endif
diff --git a/src/doc/images_collector.cpp b/src/doc/images_collector.cpp
index cd8d8adf7..2e704dfc3 100644
--- a/src/doc/images_collector.cpp
+++ b/src/doc/images_collector.cpp
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2014 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -53,13 +53,9 @@ void ImagesCollector::collectFromLayer(Layer* layer, frame_t frame)
       break;
     }
 
-    case ObjectType::LayerFolder: {
-      LayerIterator it = static_cast<LayerFolder*>(layer)->getLayerBegin();
-      LayerIterator end = static_cast<LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it)
-        collectFromLayer(*it, frame);
-
+    case ObjectType::LayerGroup: {
+      for (Layer* child : static_cast<LayerGroup*>(layer)->layers())
+        collectFromLayer(child, frame);
       break;
     }
 
diff --git a/src/doc/images_collector.h b/src/doc/images_collector.h
index 229d687b9..0029a5748 100644
--- a/src/doc/images_collector.h
+++ b/src/doc/images_collector.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
diff --git a/src/doc/layer.cpp b/src/doc/layer.cpp
index 5c98bd1c5..e0f5635d9 100644
--- a/src/doc/layer.cpp
+++ b/src/doc/layer.cpp
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -28,7 +28,7 @@ Layer::Layer(ObjectType type, Sprite* sprite)
       int(LayerFlags::Visible) |
       int(LayerFlags::Editable)))
 {
-  ASSERT(type == ObjectType::LayerImage || type == ObjectType::LayerFolder);
+  ASSERT(type == ObjectType::LayerImage || type == ObjectType::LayerGroup);
 
   setName("Layer");
 }
@@ -44,39 +44,101 @@ int Layer::getMemSize() const
 
 Layer* Layer::getPrevious() const
 {
-  if (m_parent != NULL) {
-    LayerConstIterator it =
-      std::find(m_parent->getLayerBegin(),
-                m_parent->getLayerEnd(), this);
+  if (m_parent) {
+    auto it =
+      std::find(m_parent->layers().begin(),
+                m_parent->layers().end(), this);
 
-    if (it != m_parent->getLayerEnd() &&
-        it != m_parent->getLayerBegin()) {
+    if (it != m_parent->layers().end() &&
+        it != m_parent->layers().begin()) {
       it--;
       return *it;
     }
   }
-  return NULL;
+  return nullptr;
 }
 
 Layer* Layer::getNext() const
 {
-  if (m_parent != NULL) {
-    LayerConstIterator it =
-      std::find(m_parent->getLayerBegin(),
-                m_parent->getLayerEnd(), this);
+  if (m_parent) {
+    auto it =
+      std::find(m_parent->layers().begin(),
+                m_parent->layers().end(), this);
 
-    if (it != m_parent->getLayerEnd()) {
+    if (it != m_parent->layers().end()) {
       it++;
-      if (it != m_parent->getLayerEnd())
+      if (it != m_parent->layers().end())
         return *it;
     }
   }
-  return NULL;
+  return nullptr;
+}
+
+Layer* Layer::getPreviousInWholeHierarchy() const
+{
+  // Go to children
+  if (isBrowsable())
+    return static_cast<const LayerGroup*>(this)->lastLayer();
+
+  // Go to previous layer
+  if (Layer* prev = getPrevious())
+    return prev;
+
+  // Go to previous layer in the parent
+  LayerGroup* parent = this->parent();
+  while (parent != sprite()->root() &&
+         !parent->getPrevious()) {
+    parent = parent->parent();
+  }
+  return parent->getPrevious();
+}
+
+Layer* Layer::getNextInWholeHierarchy() const
+{
+  // Go to next layer
+  if (Layer* next = getNext()) {
+    // Go to children
+    while (next->isBrowsable()) {
+      Layer* firstChild = static_cast<const LayerGroup*>(next)->firstLayer();
+      if (!firstChild)
+        break;
+      next = firstChild;
+    }
+    return next;
+  }
+
+  // Go to parent
+  if (m_sprite && parent() != m_sprite->root())
+    return m_parent;
+
+  return nullptr;
+}
+
+bool Layer::isVisibleHierarchy() const
+{
+  const Layer* layer = this;
+  while (layer) {
+    if (!layer->isVisible())
+      return false;
+    layer = layer->parent();
+  }
+  return true;
+}
+
+bool Layer::isEditableHierarchy() const
+{
+  const Layer* layer = this;
+  while (layer) {
+    if (!layer->isEditable())
+      return false;
+    layer = layer->parent();
+  }
+  return true;
 }
 
 Cel* Layer::cel(frame_t frame) const
 {
-  return NULL;
+  return nullptr;
 }
 
 //////////////////////////////////////////////////////////////////////
@@ -242,7 +304,7 @@ void LayerImage::configureAsBackground()
   switchFlags(LayerFlags::BackgroundLayerFlags, true);
   setName("Background");
 
-  sprite()->folder()->stackLayer(this, NULL);
+  sprite()->root()->stackLayer(this, NULL);
 }
 
 void LayerImage::displaceFrames(frame_t fromThis, frame_t delta)
@@ -264,90 +326,126 @@ void LayerImage::displaceFrames(frame_t fromThis, frame_t delta)
 }
 
 //////////////////////////////////////////////////////////////////////
-// LayerFolder class
+// LayerGroup class
 
-LayerFolder::LayerFolder(Sprite* sprite)
-  : Layer(ObjectType::LayerFolder, sprite)
+LayerGroup::LayerGroup(Sprite* sprite)
+  : Layer(ObjectType::LayerGroup, sprite)
 {
   setName("Layer Set");
 }
 
-LayerFolder::~LayerFolder()
+LayerGroup::~LayerGroup()
 {
   destroyAllLayers();
 }
 
-void LayerFolder::destroyAllLayers()
+void LayerGroup::destroyAllLayers()
 {
-  LayerIterator it = getLayerBegin();
-  LayerIterator end = getLayerEnd();
-
-  for (; it != end; ++it) {
-    Layer* layer = *it;
+  for (Layer* layer : m_layers)
     delete layer;
-  }
   m_layers.clear();
 }
 
-int LayerFolder::getMemSize() const
+int LayerGroup::getMemSize() const
 {
-  int size = sizeof(LayerFolder);
-  LayerConstIterator it = getLayerBegin();
-  LayerConstIterator end = getLayerEnd();
+  int size = sizeof(LayerGroup);
 
-  for (; it != end; ++it) {
-    const Layer* layer = *it;
+  for (const Layer* layer : m_layers) {
     size += layer->getMemSize();
   }
 
   return size;
 }
 
-void LayerFolder::getCels(CelList& cels) const
+void LayerGroup::allLayers(LayerList& list) const
 {
-  LayerConstIterator it = getLayerBegin();
-  LayerConstIterator end = getLayerEnd();
+  for (Layer* child : m_layers) {
+    if (child->isGroup())
+      static_cast<LayerGroup*>(child)->allLayers(list);
 
-  for (; it != end; ++it)
-    (*it)->getCels(cels);
+    list.push_back(child);
+  }
 }
 
-void LayerFolder::addLayer(Layer* layer)
+layer_t LayerGroup::allLayersCount() const
+{
+  layer_t count = 0;
+  for (Layer* child : m_layers) {
+    if (child->isGroup())
+      count += static_cast<LayerGroup*>(child)->allLayersCount();
+    ++count;
+  }
+  return count;
+}
+
+void LayerGroup::allVisibleLayers(LayerList& list) const
+{
+  for (Layer* child : m_layers) {
+    if (!child->isVisible())
+      continue;
+
+    if (child->isGroup())
+      static_cast<LayerGroup*>(child)->allVisibleLayers(list);
+
+    list.push_back(child);
+  }
+}
+
+void LayerGroup::allBrowsableLayers(LayerList& list) const
+{
+  for (Layer* child : m_layers) {
+    if (child->isBrowsable())
+      static_cast<LayerGroup*>(child)->allBrowsableLayers(list);
+
+    list.push_back(child);
+  }
+}
+
+void LayerGroup::getCels(CelList& cels) const
+{
+  for (const Layer* layer : m_layers)
+    layer->getCels(cels);
+}
+
+void LayerGroup::addLayer(Layer* layer)
 {
   m_layers.push_back(layer);
   layer->setParent(this);
 }
 
-void LayerFolder::removeLayer(Layer* layer)
+void LayerGroup::removeLayer(Layer* layer)
 {
-  LayerIterator it = std::find(m_layers.begin(), m_layers.end(), layer);
+  auto it = std::find(m_layers.begin(), m_layers.end(), layer);
   ASSERT(it != m_layers.end());
   m_layers.erase(it);
 
-  layer->setParent(NULL);
+  layer->setParent(nullptr);
 }
 
-void LayerFolder::stackLayer(Layer* layer, Layer* after)
+void LayerGroup::insertLayer(Layer* layer, Layer* after)
+{
+  auto after_it = m_layers.begin();
+  if (after) {
+    after_it = std::find(m_layers.begin(), m_layers.end(), after);
+    if (after_it != m_layers.end())
+      ++after_it;
+  }
+  m_layers.insert(after_it, layer);
+
+  layer->setParent(this);
+}
+
+void LayerGroup::stackLayer(Layer* layer, Layer* after)
 {
   ASSERT(layer != after);
   if (layer == after)
     return;
 
-  LayerIterator it = std::find(m_layers.begin(), m_layers.end(), layer);
-  ASSERT(it != m_layers.end());
-  m_layers.erase(it);
-
-  if (after) {
-    LayerIterator after_it = std::find(m_layers.begin(), m_layers.end(), after);
-    ASSERT(after_it != m_layers.end());
-    after_it++;
-    m_layers.insert(after_it, layer);
-  }
-  else
-    m_layers.insert(m_layers.begin(), layer);
+  removeLayer(layer);
+  insertLayer(layer, after);
 }
 
-void LayerFolder::displaceFrames(frame_t fromThis, frame_t delta)
+void LayerGroup::displaceFrames(frame_t fromThis, frame_t delta)
 {
   for (Layer* layer : m_layers)
     layer->displaceFrames(fromThis, delta);
diff --git a/src/doc/layer.h b/src/doc/layer.h
index a27896505..72db1079c 100644
--- a/src/doc/layer.h
+++ b/src/doc/layer.h
@@ -24,17 +24,19 @@ namespace doc {
   class Sprite;
   class Layer;
   class LayerImage;
-  class LayerFolder;
+  class LayerGroup;
 
   //////////////////////////////////////////////////////////////////////
   // Layer class
 
   enum class LayerFlags {
+    None       = 0,
     Visible    = 1,             // Can be read
     Editable   = 2,             // Can be written
     LockMove   = 4,             // Cannot be moved
     Background = 8,             // Stack order cannot be changed
     Continuous = 16,            // Prefer to link cels when the user copy them
+    Collapsed  = 32,            // Prefer to show this group layer collapsed
 
     BackgroundLayerFlags = LockMove | Background,
   };
@@ -52,15 +54,19 @@ namespace doc {
     void setName(const std::string& name) { m_name = name; }
 
     Sprite* sprite() const { return m_sprite; }
-    LayerFolder* parent() const { return m_parent; }
-    void setParent(LayerFolder* folder) { m_parent = folder; }
+    LayerGroup* parent() const { return m_parent; }
+    void setParent(LayerGroup* group) { m_parent = group; }
 
     // Gets the previous sibling of this layer.
     Layer* getPrevious() const;
     Layer* getNext() const;
 
+    Layer* getPreviousInWholeHierarchy() const;
+    Layer* getNextInWholeHierarchy() const;
+
     bool isImage() const { return type() == ObjectType::LayerImage; }
-    bool isFolder() const { return type() == ObjectType::LayerFolder; }
+    bool isGroup() const { return type() == ObjectType::LayerGroup; }
+    virtual bool isBrowsable() const { return false; }
 
     bool isBackground() const  { return hasFlags(LayerFlags::Background); }
     bool isTransparent() const { return !hasFlags(LayerFlags::Background); }
@@ -68,12 +74,18 @@ namespace doc {
     bool isEditable() const    { return hasFlags(LayerFlags::Editable); }
     bool isMovable() const     { return !hasFlags(LayerFlags::LockMove); }
     bool isContinuous() const  { return hasFlags(LayerFlags::Continuous); }
+    bool isCollapsed() const   { return hasFlags(LayerFlags::Collapsed); }
+    bool isExpanded() const    { return !hasFlags(LayerFlags::Collapsed); }
+
+    bool isVisibleHierarchy() const;
+    bool isEditableHierarchy() const;
 
     void setBackground(bool state) { switchFlags(LayerFlags::Background, state); }
     void setVisible   (bool state) { switchFlags(LayerFlags::Visible, state); }
     void setEditable  (bool state) { switchFlags(LayerFlags::Editable, state); }
     void setMovable   (bool state) { switchFlags(LayerFlags::LockMove, !state); }
     void setContinuous(bool state) { switchFlags(LayerFlags::Continuous, state); }
+    void setCollapsed (bool state) { switchFlags(LayerFlags::Collapsed, state); }
 
     LayerFlags flags() const {
       return m_flags;
@@ -101,7 +113,7 @@ namespace doc {
   private:
     std::string m_name;           // layer name
     Sprite* m_sprite;             // owner of the layer
-    LayerFolder* m_parent;        // parent layer
+    LayerGroup* m_parent;        // parent layer
     LayerFlags m_flags;           // stack order cannot be changed
 
     // Disable assigment
@@ -154,32 +166,38 @@ namespace doc {
   };
 
   //////////////////////////////////////////////////////////////////////
-  // LayerFolder class
+  // LayerGroup class
 
-  class LayerFolder : public Layer {
+  class LayerGroup : public Layer {
   public:
-    explicit LayerFolder(Sprite* sprite);
-    virtual ~LayerFolder();
+    explicit LayerGroup(Sprite* sprite);
+    virtual ~LayerGroup();
 
     virtual int getMemSize() const override;
 
-    const LayerList& getLayersList() { return m_layers; }
-    LayerIterator getLayerBegin() { return m_layers.begin(); }
-    LayerIterator getLayerEnd() { return m_layers.end(); }
-    LayerConstIterator getLayerBegin() const { return m_layers.begin(); }
-    LayerConstIterator getLayerEnd() const { return m_layers.end(); }
-    int getLayersCount() const { return (int)m_layers.size(); }
+    const LayerList& layers() const { return m_layers; }
+    int layersCount() const { return (int)m_layers.size(); }
 
     void addLayer(Layer* layer);
     void removeLayer(Layer* layer);
+    void insertLayer(Layer* layer, Layer* after);
     void stackLayer(Layer* layer, Layer* after);
 
-    Layer* getFirstLayer() { return (m_layers.empty() ? NULL: m_layers.front()); }
-    Layer* getLastLayer() { return (m_layers.empty() ? NULL: m_layers.back()); }
+    Layer* firstLayer() const { return (m_layers.empty() ? nullptr: m_layers.front()); }
+    Layer* lastLayer() const { return (m_layers.empty() ? nullptr: m_layers.back()); }
+
+    void allLayers(LayerList& list) const;
+    layer_t allLayersCount() const;
+    void allVisibleLayers(LayerList& list) const;
+    void allBrowsableLayers(LayerList& list) const;
 
     void getCels(CelList& cels) const override;
     void displaceFrames(frame_t fromThis, frame_t delta) override;
 
+    bool isBrowsable() const override {
+      return isGroup() && isExpanded() && !m_layers.empty();
+    }
+
   private:
     void destroyAllLayers();
 
diff --git a/src/doc/layer_index.cpp b/src/doc/layer_index.cpp
deleted file mode 100644
index 0b1bdb828..000000000
--- a/src/doc/layer_index.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-// Aseprite Document Library
-// Copyright (c) 2001-2014 David Capello
-//
-// This file is released under the terms of the MIT license.
-// Read LICENSE.txt for more information.
-
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include "doc/layer_index.h"
-
-namespace doc {
-
-const LayerIndex LayerIndex::NoLayer(-1);
-
-} // namespace doc
diff --git a/src/doc/layer_index.h b/src/doc/layer_index.h
deleted file mode 100644
index af3393c65..000000000
--- a/src/doc/layer_index.h
+++ /dev/null
@@ -1,54 +0,0 @@
-// Aseprite Document Library
-// Copyright (c) 2001-2014 David Capello
-//
-// This file is released under the terms of the MIT license.
-// Read LICENSE.txt for more information.
-
-#ifndef DOC_LAYER_INDEX_H_INCLUDED
-#define DOC_LAYER_INDEX_H_INCLUDED
-#pragma once
-
-namespace doc {
-
-  class LayerIndex {
-  public:
-    static const LayerIndex NoLayer;
-
-    LayerIndex() : m_value(0) { }
-    explicit LayerIndex(int value) : m_value(value) { }
-
-    LayerIndex next(int i = 1) const { return LayerIndex(m_value+i); };
-    LayerIndex previous(int i = 1) const { return LayerIndex(m_value-i); };
-
-    operator int() { return m_value; }
-    operator const int() const { return m_value; }
-
-    LayerIndex& operator=(const LayerIndex& o) { m_value = o.m_value; return *this; }
-    LayerIndex& operator++() { ++m_value; return *this; }
-    LayerIndex& operator--() { --m_value; return *this; }
-    LayerIndex operator++(int) { LayerIndex old(*this); ++m_value; return old; }
-    LayerIndex operator--(int) { LayerIndex old(*this); --m_value; return old; }
-    LayerIndex& operator+=(const LayerIndex& o) { m_value += o.m_value; return *this; }
-    LayerIndex& operator-=(const LayerIndex& o) { m_value -= o.m_value; return *this; }
-    bool operator<(const LayerIndex& o) const { return m_value < o.m_value; }
-    bool operator>(const LayerIndex& o) const { return m_value > o.m_value; }
-    bool operator<=(const LayerIndex& o) const { return m_value <= o.m_value; }
-    bool operator>=(const LayerIndex& o) const { return m_value >= o.m_value; }
-    bool operator==(const LayerIndex& o) const { return m_value == o.m_value; }
-    bool operator!=(const LayerIndex& o) const { return m_value != o.m_value; }
-
-  private:
-    int m_value;
-  };
-
-  inline LayerIndex operator+(const LayerIndex& x, const LayerIndex& y) {
-    return LayerIndex((int)x + (int)y);
-  }
-
-  inline LayerIndex operator-(const LayerIndex& x, const LayerIndex& y) {
-    return LayerIndex((int)x - (int)y);
-  }
-
-} // namespace doc
-
-#endif
diff --git a/src/doc/layer_io.cpp b/src/doc/layer_io.cpp
index 066b03457..e56a59bf8 100644
--- a/src/doc/layer_io.cpp
+++ b/src/doc/layer_io.cpp
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -87,15 +87,12 @@ void write_layer(std::ostream& os, const Layer* layer)
       break;
     }
 
-    case ObjectType::LayerFolder: {
-      LayerConstIterator it = static_cast<const LayerFolder*>(layer)->getLayerBegin();
-      LayerConstIterator end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
+    case ObjectType::LayerGroup: {
       // Number of sub-layers
-      write16(os, static_cast<const LayerFolder*>(layer)->getLayersCount());
+      write16(os, static_cast<const LayerGroup*>(layer)->layersCount());
 
-      for (; it != end; ++it)
-        write_layer(os, *it);
+      for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers())
+        write_layer(os, child);
       break;
     }
 
@@ -150,16 +147,16 @@ Layer* read_layer(std::istream& is, SubObjectsFromSprite* subObjects)
       break;
     }
 
-    case ObjectType::LayerFolder: {
+    case ObjectType::LayerGroup: {
       // Create the layer set
-      layer.reset(new LayerFolder(subObjects->sprite()));
+      layer.reset(new LayerGroup(subObjects->sprite()));
 
       // Number of sub-layers
       int layers = read16(is);
       for (int c=0; c<layers; c++) {
         Layer* child = read_layer(is, subObjects);
         if (child)
-          static_cast<LayerFolder*>(layer.get())->addLayer(child);
+          static_cast<LayerGroup*>(layer.get())->addLayer(child);
         else
           break;
       }
diff --git a/src/doc/layer_list.cpp b/src/doc/layer_list.cpp
new file mode 100644
index 000000000..584936f8d
--- /dev/null
+++ b/src/doc/layer_list.cpp
@@ -0,0 +1,54 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "doc/layer.h"
+#include "doc/layer_list.h"
+
+#include <algorithm>
+
+namespace doc {
+
+layer_t find_layer_index(const LayerList& layers, const Layer* layer)
+{
+  auto it = std::find(layers.begin(), layers.end(), layer);
+  if (it != layers.end())
+    return it - layers.begin();
+  else
+    return 0;
+}
+
+bool are_layers_adjacent(const LayerList& layers)
+{
+  layer_t count = 0;
+  Layer* prev = nullptr;
+  for (auto layer : layers) {
+    if (prev && prev != layer->getPrevious())
+      break;
+    prev = layer;
+    ++count;
+  }
+  if (count == layers.size())
+    return true;
+
+  count = 0;
+  prev = nullptr;
+  for (auto layer : layers) {
+    if (prev && prev != layer->getNext())
+      break;
+    prev = layer;
+    ++count;
+  }
+  if (count == layers.size())
+    return true;
+
+  return false;
+}
+
+} // namespace doc
diff --git a/src/doc/layer_list.h b/src/doc/layer_list.h
index 82aaa5790..88adc8793 100644
--- a/src/doc/layer_list.h
+++ b/src/doc/layer_list.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -15,8 +15,10 @@ namespace doc {
   class Layer;
 
   typedef std::vector<Layer*> LayerList;
-  typedef LayerList::iterator LayerIterator;
-  typedef LayerList::const_iterator LayerConstIterator;
+  typedef int layer_t;
+
+  layer_t find_layer_index(const LayerList& layers, const Layer* layer);
+  bool are_layers_adjacent(const LayerList& layers);
 
 } // namespace doc
 
diff --git a/src/doc/layer_list_tests.cpp b/src/doc/layer_list_tests.cpp
new file mode 100644
index 000000000..5081d8b9f
--- /dev/null
+++ b/src/doc/layer_list_tests.cpp
@@ -0,0 +1,65 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gtest/gtest.h>
+
+#include "base/unique_ptr.h"
+#include "doc/layer.h"
+#include "doc/layer_list.h"
+#include "doc/sprite.h"
+
+#include <algorithm>
+
+using namespace doc;
+
+TEST(LayerList, AreLayersAdjacent)
+{
+  base::UniquePtr<Sprite> spr(new Sprite(IMAGE_RGB, 32, 32, 256));
+  LayerGroup* root = spr->root();
+  Layer* layer1 = new LayerImage(spr);
+  Layer* layer2 = new LayerImage(spr);
+  Layer* layer3 = new LayerImage(spr);
+  Layer* layer4 = new LayerImage(spr);
+  root->addLayer(layer1);
+  root->addLayer(layer2);
+  root->addLayer(layer3);
+  root->addLayer(layer4);
+
+  LayerList layers;
+  root->allLayers(layers);
+  EXPECT_EQ(4, layers.size());
+  EXPECT_TRUE(are_layers_adjacent(layers));
+
+  std::reverse(layers.begin(), layers.end());
+  EXPECT_EQ(4, layers.size());
+  EXPECT_TRUE(are_layers_adjacent(layers));
+
+  layers.erase(layers.begin());
+  EXPECT_EQ(3, layers.size());
+  EXPECT_TRUE(are_layers_adjacent(layers));
+
+  layers.erase(layers.begin()+1);
+  EXPECT_EQ(2, layers.size());
+  EXPECT_FALSE(are_layers_adjacent(layers));
+
+  std::reverse(layers.begin(), layers.end());
+  EXPECT_EQ(2, layers.size());
+  EXPECT_FALSE(are_layers_adjacent(layers));
+
+  layers.erase(layers.begin());
+  EXPECT_EQ(1, layers.size());
+  EXPECT_TRUE(are_layers_adjacent(layers));
+}
+
+int main(int argc, char** argv)
+{
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
diff --git a/src/doc/layers_range.cpp b/src/doc/layers_range.cpp
deleted file mode 100644
index a2f310494..000000000
--- a/src/doc/layers_range.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-// Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
-//
-// This file is released under the terms of the MIT license.
-// Read LICENSE.txt for more information.
-
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include "doc/layers_range.h"
-
-#include "doc/cel.h"
-#include "doc/layer.h"
-#include "doc/sprite.h"
-
-namespace doc {
-
-LayersRange::LayersRange(const Sprite* sprite,
-                         LayerIndex first, LayerIndex last)
-  : m_begin(sprite, first, last)
-  , m_end()
-{
-}
-
-LayersRange::iterator::iterator()
-  : m_layer(nullptr)
-  , m_cur(-1)
-  , m_last(-1)
-{
-}
-
-LayersRange::iterator::iterator(const Sprite* sprite,
-                                LayerIndex first, LayerIndex last)
-  : m_layer(nullptr)
-  , m_cur(first)
-  , m_last(last)
-{
-  m_layer = sprite->layer(first);
-}
-
-LayersRange::iterator& LayersRange::iterator::operator++()
-{
-  if (!m_layer)
-    return *this;
-
-  ++m_cur;
-  if (m_cur > m_last)
-    m_layer = nullptr;
-  else
-    m_layer = m_layer->getNext();
-
-  return *this;
-}
-
-} // namespace doc
diff --git a/src/doc/layers_range.h b/src/doc/layers_range.h
deleted file mode 100644
index 3fba454d2..000000000
--- a/src/doc/layers_range.h
+++ /dev/null
@@ -1,58 +0,0 @@
-// Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
-//
-// This file is released under the terms of the MIT license.
-// Read LICENSE.txt for more information.
-
-#ifndef DOC_LAYERS_RANGE_H_INCLUDED
-#define DOC_LAYERS_RANGE_H_INCLUDED
-#pragma once
-
-#include "doc/layer_index.h"
-#include "doc/object_id.h"
-
-#include <set>
-
-namespace doc {
-  class Layer;
-  class Sprite;
-
-  class LayersRange {
-  public:
-    LayersRange(const Sprite* sprite, LayerIndex first, LayerIndex last);
-
-    class iterator {
-    public:
-      iterator();
-      iterator(const Sprite* sprite, LayerIndex first, LayerIndex last);
-
-      bool operator==(const iterator& other) const {
-        return m_layer == other.m_layer;
-      }
-
-      bool operator!=(const iterator& other) const {
-        return !operator==(other);
-      }
-
-      Layer* operator*() const {
-        return m_layer;
-      }
-
-      iterator& operator++();
-
-    private:
-      Layer* m_layer;
-      LayerIndex m_cur, m_last;
-      std::set<ObjectId> m_visited;
-    };
-
-    iterator begin() { return m_begin; }
-    iterator end() { return m_end; }
-
-  private:
-    iterator m_begin, m_end;
-  };
-
-} // namespace doc
-
-#endif
diff --git a/src/doc/object_type.h b/src/doc/object_type.h
index cb7dcaf14..60cb53f4f 100644
--- a/src/doc/object_type.h
+++ b/src/doc/object_type.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -20,7 +20,7 @@ namespace doc {
     Cel,
     CelData,
     LayerImage,
-    LayerFolder,
+    LayerGroup,
     Sprite,
     Document,
     FrameTag,
diff --git a/src/doc/selected_frames.cpp b/src/doc/selected_frames.cpp
new file mode 100644
index 000000000..64639bf8a
--- /dev/null
+++ b/src/doc/selected_frames.cpp
@@ -0,0 +1,106 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "doc/selected_frames.h"
+
+#include <algorithm>
+
+namespace doc {
+
+std::size_t SelectedFrames::size() const
+{
+  std::size_t size = 0;
+  for (auto& range : m_ranges)
+    size += (range.toFrame - range.fromFrame + 1);
+  return size;
+}
+
+void SelectedFrames::clear()
+{
+  m_ranges.clear();
+}
+
+void SelectedFrames::insert(frame_t frame)
+{
+  ASSERT(frame >= 0);
+
+  if (m_ranges.empty()) {
+    m_ranges.push_back(FrameRange(frame));
+    return;
+  }
+
+  auto it = m_ranges.begin();
+  auto end = m_ranges.end();
+  auto next = it;
+
+  for (; it!=end; it=next) {
+    if (frame >= it->fromFrame &&
+        frame <= it->toFrame)
+      break;
+
+    if (frame < it->fromFrame) {
+      if (frame == it->fromFrame-1)
+        --it->fromFrame;
+      else
+        m_ranges.insert(it, FrameRange(frame));
+      break;
+    }
+
+    ++next;
+
+    if (frame > it->toFrame && (next == end || frame < next->fromFrame-1)) {
+      if (frame == it->toFrame+1)
+        ++it->toFrame;
+      else
+        m_ranges.insert(next, FrameRange(frame));
+      break;
+    }
+  }
+}
+
+void SelectedFrames::insert(frame_t fromFrame, frame_t toFrame)
+{
+  if (fromFrame > toFrame)
+    std::swap(fromFrame, toFrame);
+
+  // TODO improve this
+  for (frame_t frame = fromFrame; frame <= toFrame; ++frame) {
+    insert(frame);
+  }
+}
+
+bool SelectedFrames::contains(frame_t frame) const
+{
+  return std::binary_search(
+    m_ranges.begin(),
+    m_ranges.end(),
+    FrameRange(frame),
+    [](const FrameRange& a,
+       const FrameRange& b) -> bool {
+      return (a.toFrame < b.fromFrame);
+    });
+}
+
+void SelectedFrames::displace(frame_t frameDelta)
+{
+  // Avoid setting negative numbers in frame ranges
+  if (firstFrame()+frameDelta < 0)
+    frameDelta = -firstFrame();
+
+  for (auto& range : m_ranges) {
+    range.fromFrame += frameDelta;
+    range.toFrame += frameDelta;
+
+    ASSERT(range.fromFrame >= 0);
+    ASSERT(range.toFrame >= 0);
+  }
+}
+
+} // namespace doc
diff --git a/src/doc/selected_frames.h b/src/doc/selected_frames.h
new file mode 100644
index 000000000..56967c76f
--- /dev/null
+++ b/src/doc/selected_frames.h
@@ -0,0 +1,150 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef DOC_SELECTED_FRAMES_H_INCLUDED
+#define DOC_SELECTED_FRAMES_H_INCLUDED
+#pragma once
+
+#include "doc/frame_range.h"
+
+#include <iterator>
+#include <vector>
+
+namespace doc {
+
+  class SelectedFrames {
+    typedef std::vector<FrameRange> Ranges;
+
+  public:
+    class const_iterator : public std::iterator<std::forward_iterator_tag, frame_t> {
+    public:
+      const_iterator(const Ranges::const_iterator& it)
+        : m_it(it), m_frame(-1) {
+      }
+
+      const_iterator& operator++() {
+        if (m_frame < 0)
+          m_frame = m_it->fromFrame;
+
+        if (m_frame < m_it->toFrame)
+          ++m_frame;
+        else {
+          m_frame = -1;
+          ++m_it;
+        }
+
+        return *this;
+      }
+
+      frame_t operator*() const {
+        if (m_frame < 0)
+          m_frame = m_it->fromFrame;
+        return m_frame;
+      }
+
+      bool operator==(const const_iterator& o) const {
+        return (m_it == o.m_it && m_frame == o.m_frame);
+      }
+
+      bool operator!=(const const_iterator& it) const {
+        return !operator==(it);
+      }
+
+    private:
+      mutable Ranges::const_iterator m_it;
+      mutable frame_t m_frame;
+    };
+
+    class const_reverse_iterator : public std::iterator<std::forward_iterator_tag, frame_t> {
+    public:
+      const_reverse_iterator(const Ranges::const_reverse_iterator& it)
+        : m_it(it), m_frame(-1) {
+      }
+
+      const_reverse_iterator& operator++() {
+        if (m_frame < 0)
+          m_frame = m_it->toFrame;
+
+        if (m_frame > m_it->fromFrame)
+          --m_frame;
+        else {
+          m_frame = -1;
+          ++m_it;
+        }
+
+        return *this;
+      }
+
+      frame_t operator*() const {
+        if (m_frame < 0)
+          m_frame = m_it->toFrame;
+        return m_frame;
+      }
+
+      bool operator==(const const_reverse_iterator& o) const {
+        return (m_it == o.m_it && m_frame == o.m_frame);
+      }
+
+      bool operator!=(const const_reverse_iterator& it) const {
+        return !operator==(it);
+      }
+
+    private:
+      mutable Ranges::const_reverse_iterator m_it;
+      mutable frame_t m_frame;
+    };
+
+    class Reversed {
+    public:
+      typedef const_reverse_iterator const_iterator;
+
+      const_iterator begin() const { return m_selectedFrames.rbegin(); }
+      const_iterator end() const { return m_selectedFrames.rend(); }
+
+      Reversed(const SelectedFrames& selectedFrames)
+        : m_selectedFrames(selectedFrames) {
+      }
+
+    private:
+      const SelectedFrames& m_selectedFrames;
+    };
+
+    const_iterator begin() const { return const_iterator(m_ranges.begin()); }
+    const_iterator end() const { return const_iterator(m_ranges.end()); }
+    const_reverse_iterator rbegin() const { return const_reverse_iterator(m_ranges.rbegin()); }
+    const_reverse_iterator rend() const { return const_reverse_iterator(m_ranges.rend()); }
+
+    std::size_t size() const;
+    std::size_t ranges() const { return m_ranges.size(); }
+    bool empty() const { return m_ranges.empty(); }
+
+    void clear();
+    void insert(frame_t frame);
+    void insert(frame_t fromFrame, frame_t toFrame);
+
+    bool contains(frame_t frame) const;
+
+    frame_t firstFrame() const { return (!m_ranges.empty() ? m_ranges.front().fromFrame: -1); }
+    frame_t lastFrame() const { return (!m_ranges.empty() ? m_ranges.back().toFrame: -1); }
+
+    void displace(frame_t frameDelta);
+    Reversed reversed() const { return Reversed(*this); }
+
+    bool operator==(const SelectedFrames& o) const {
+      return m_ranges == o.m_ranges;
+    }
+
+    bool operator!=(const SelectedFrames& o) const {
+      return !operator==(o);
+    }
+
+  private:
+    Ranges m_ranges;
+  };
+
+} // namespace doc
+
+#endif  // DOC_SELECTED_FRAMES_H_INCLUDED
diff --git a/src/doc/selected_frames_tests.cpp b/src/doc/selected_frames_tests.cpp
new file mode 100644
index 000000000..a579e7972
--- /dev/null
+++ b/src/doc/selected_frames_tests.cpp
@@ -0,0 +1,130 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gtest/gtest.h>
+
+#include "doc/selected_frames.h"
+
+#include <algorithm>
+#include <iterator>
+
+using namespace doc;
+
+TEST(SelectedFrames, BasicOneRange)
+{
+  SelectedFrames f;
+  EXPECT_TRUE(f.empty());
+  f.insert(1);
+  f.insert(2);
+  f.insert(3);
+  EXPECT_FALSE(f.empty());
+  EXPECT_EQ(3, f.size());
+  EXPECT_EQ(1, f.ranges());
+
+  std::vector<frame_t> res;
+  std::copy(f.begin(), f.end(), std::back_inserter(res));
+
+  ASSERT_EQ(3, res.size());
+  EXPECT_EQ(1, res[0]);
+  EXPECT_EQ(2, res[1]);
+  EXPECT_EQ(3, res[2]);
+}
+
+TEST(SelectedFrames, BasicThreeRanges)
+{
+  SelectedFrames f;
+  f.insert(1);
+  f.insert(3);
+  f.insert(5);
+  EXPECT_EQ(3, f.size());
+  EXPECT_EQ(3, f.ranges());
+
+  std::vector<frame_t> res;
+  std::copy(f.begin(), f.end(), std::back_inserter(res));
+
+  ASSERT_EQ(3, res.size());
+  EXPECT_EQ(1, res[0]);
+  EXPECT_EQ(3, res[1]);
+  EXPECT_EQ(5, res[2]);
+}
+
+TEST(SelectedFrames, InsertSelectedFrameInsideSelectedRange)
+{
+  SelectedFrames f;
+  f.insert(3);
+  f.insert(5, 8);
+  f.insert(7);
+  EXPECT_EQ(5, f.size());
+  EXPECT_EQ(2, f.ranges());
+  EXPECT_EQ(3, f.firstFrame());
+  EXPECT_EQ(8, f.lastFrame());
+
+  std::vector<frame_t> res;
+  std::copy(f.begin(), f.end(), std::back_inserter(res));
+
+  ASSERT_EQ(5, res.size());
+  EXPECT_EQ(3, res[0]);
+  EXPECT_EQ(5, res[1]);
+  EXPECT_EQ(6, res[2]);
+  EXPECT_EQ(7, res[3]);
+  EXPECT_EQ(8, res[4]);
+}
+
+TEST(SelectedFrames, Contains)
+{
+  SelectedFrames f;
+  f.insert(1);
+  f.insert(4, 5);
+  f.insert(7, 9);
+  EXPECT_EQ(6, f.size());
+  EXPECT_EQ(3, f.ranges());
+
+  EXPECT_FALSE(f.contains(0));
+  EXPECT_TRUE(f.contains(1));
+  EXPECT_FALSE(f.contains(2));
+  EXPECT_FALSE(f.contains(3));
+  EXPECT_TRUE(f.contains(4));
+  EXPECT_TRUE(f.contains(5));
+  EXPECT_FALSE(f.contains(6));
+  EXPECT_TRUE(f.contains(7));
+  EXPECT_TRUE(f.contains(8));
+  EXPECT_TRUE(f.contains(9));
+  EXPECT_FALSE(f.contains(10));
+}
+
+TEST(SelectedFrames, ReverseIterators)
+{
+  SelectedFrames f;
+  f.insert(1);
+  f.insert(5, 7);
+  EXPECT_EQ(4, f.size());
+  EXPECT_EQ(2, f.ranges());
+
+  std::vector<frame_t> res;
+  std::copy(f.rbegin(), f.rend(), std::back_inserter(res));
+
+  ASSERT_EQ(4, res.size());
+  EXPECT_EQ(7, res[0]);
+  EXPECT_EQ(6, res[1]);
+  EXPECT_EQ(5, res[2]);
+  EXPECT_EQ(1, res[3]);
+
+  std::vector<frame_t> res2;
+  for (frame_t frame : f.reversed())
+    res2.push_back(frame);
+
+  EXPECT_EQ(res, res2);
+}
+
+int main(int argc, char** argv)
+{
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
diff --git a/src/doc/selected_layers.cpp b/src/doc/selected_layers.cpp
new file mode 100644
index 000000000..c86f53e4c
--- /dev/null
+++ b/src/doc/selected_layers.cpp
@@ -0,0 +1,142 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "doc/selected_layers.h"
+
+#include "doc/layer.h"
+#include "doc/sprite.h"
+
+namespace doc {
+
+void SelectedLayers::clear()
+{
+  m_set.clear();
+}
+
+void SelectedLayers::insert(Layer* layer)
+{
+  ASSERT(layer);
+  m_set.insert(layer);
+}
+
+void SelectedLayers::erase(Layer* layer)
+{
+  m_set.erase(layer);
+}
+
+bool SelectedLayers::contains(Layer* layer) const
+{
+  return m_set.find(layer) != m_set.end();
+}
+
+bool SelectedLayers::hasSameParent() const
+{
+  Layer* parent = nullptr;
+  for (auto layer : *this) {
+    if (parent) {
+      if (layer->parent() != parent)
+        return false;
+    }
+    else
+      parent = layer->parent();
+  }
+  return true;
+}
+
+LayerList SelectedLayers::toLayerList() const
+{
+  LayerList output;
+
+  if (empty())
+    return output;
+
+  ASSERT(*begin());
+  ASSERT((*begin())->sprite());
+
+  for (Layer* layer = (*begin())->sprite()->firstBrowsableLayer();
+       layer != nullptr;
+       layer = layer->getNextInWholeHierarchy()) {
+    if (contains(layer))
+      output.push_back(layer);
+  }
+
+  return output;
+}
+
+void SelectedLayers::removeChildrenIfParentIsSelected()
+{
+  SelectedLayers removeThese;
+
+  for (Layer* child : *this) {
+    Layer* parent = child->parent();
+    while (parent) {
+      if (contains(parent)) {
+        removeThese.insert(child);
+        break;
+      }
+      parent = parent->parent();
+    }
+  }
+
+  for (Layer* child : removeThese)
+    erase(child);
+}
+
+void SelectedLayers::selectAllLayers(LayerGroup* group)
+{
+  for (Layer* layer : group->layers()) {
+    if (layer->isGroup())
+      selectAllLayers(static_cast<LayerGroup*>(layer));
+    insert(layer);
+  }
+}
+
+void SelectedLayers::displace(layer_t layerDelta)
+{
+  // Do nothing case
+  if (layerDelta == 0)
+    return;
+
+  const SelectedLayers original = *this;
+
+retry:;
+  clear();
+
+  for (auto it : original) {
+    Layer* layer = it;
+
+    if (layerDelta > 0) {
+      for (layer_t i=0; layer && i<layerDelta; ++i)
+        layer = layer->getNextInWholeHierarchy();
+    }
+    else if (layerDelta < 0) {
+      for (layer_t i=0; layer && i>layerDelta; --i) {
+        layer = layer->getPreviousInWholeHierarchy();
+      }
+    }
+
+    if (layer) {
+      insert(layer);
+    }
+    // If some layer is outside the range it means that the delta is
+    // too big (out of bounds), we reduce the delta and try again the
+    // whole process.
+    else {
+      layerDelta -= SGN(layerDelta);
+      if (layerDelta == 0) {
+        m_set = original.m_set;
+        break;
+      }
+      goto retry;
+    }
+  }
+}
+
+} // namespace doc
diff --git a/src/doc/selected_layers.h b/src/doc/selected_layers.h
new file mode 100644
index 000000000..7d2a4ed2f
--- /dev/null
+++ b/src/doc/selected_layers.h
@@ -0,0 +1,59 @@
+// Aseprite Document Library
+// Copyright (c) 2016 David Capello
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef DOC_SELECTED_LAYERS_H_INCLUDED
+#define DOC_SELECTED_LAYERS_H_INCLUDED
+#pragma once
+
+#include <set>
+#include "layer_list.h"
+
+namespace doc {
+
+  class Layer;
+  class LayerGroup;
+
+  class SelectedLayers {
+  public:
+    typedef std::set<Layer*> Set;
+    typedef Set::iterator iterator;
+    typedef Set::const_iterator const_iterator;
+
+    iterator begin() { return m_set.begin(); }
+    iterator end() { return m_set.end(); }
+    const_iterator begin() const { return m_set.begin(); }
+    const_iterator end() const { return m_set.end(); }
+
+    bool empty() const { return m_set.empty(); }
+    layer_t size() const { return m_set.size(); }
+
+    void clear();
+    void insert(Layer* layer);
+    void erase(Layer* layer);
+
+    bool contains(Layer* layer) const;
+    bool hasSameParent() const;
+    LayerList toLayerList() const;
+
+    void removeChildrenIfParentIsSelected();
+    void selectAllLayers(LayerGroup* group);
+    void displace(layer_t layerDelta);
+
+    bool operator==(const SelectedLayers& o) const {
+      return m_set == o.m_set;
+    }
+
+    bool operator!=(const SelectedLayers& o) const {
+      return !operator==(o);
+    }
+
+  private:
+    Set m_set;
+  };
+
+} // namespace doc
+
+#endif  // DOC_SELECTED_LAYERS_H_INCLUDED
diff --git a/src/doc/site.cpp b/src/doc/site.cpp
index e65e74fd4..9efb8e302 100644
--- a/src/doc/site.cpp
+++ b/src/doc/site.cpp
@@ -17,18 +17,6 @@
 
 namespace doc {
 
-LayerIndex Site::layerIndex() const
-{
-  return (m_sprite && m_layer ?
-          m_sprite->layerToIndex(m_layer): LayerIndex());
-}
-
-void Site::layerIndex(LayerIndex layerIndex)
-{
-  ASSERT(m_sprite != NULL);
-  m_layer = m_sprite->indexToLayer(layerIndex);
-}
-
 Palette* Site::palette()
 {
   return (m_sprite ? m_sprite->palette(m_frame): NULL);
diff --git a/src/doc/site.h b/src/doc/site.h
index d1b051944..872172507 100644
--- a/src/doc/site.h
+++ b/src/doc/site.h
@@ -9,7 +9,8 @@
 #pragma once
 
 #include "doc/frame.h"
-#include "doc/layer_index.h"
+#include "doc/selected_frames.h"
+#include "doc/selected_layers.h"
 
 namespace doc {
 
@@ -25,12 +26,33 @@ namespace doc {
   // etc.).
   class Site {
   public:
+    // Were is the user focus. E.g. If this focus is in the timeline,
+    // it means that commands should applied in the context of the
+    // timeline (layers, or frames, or cels).
+    enum Focus {
+      None,
+      InEditor,
+      InLayers,
+      InFrames,
+      InCels,
+      InColorBar
+    };
+
     Site()
-      : m_document(nullptr)
+      : m_focus(None)
+      , m_document(nullptr)
       , m_sprite(nullptr)
       , m_layer(nullptr)
       , m_frame(0) { }
 
+    const Focus focus() const { return m_focus; }
+    bool inEditor() const { return m_focus == InEditor; }
+    bool inLayers() const { return m_focus == InLayers; }
+    bool inFrames() const { return m_focus == InFrames; }
+    bool inCels() const { return m_focus == InCels; }
+    bool inColorBar() const { return m_focus == InColorBar; }
+    bool inTimeline() const { return (inLayers() || inFrames() || inCels()); }
+
     const Document* document() const { return m_document; }
     const Sprite* sprite() const { return m_sprite; }
     const Layer* layer() const { return m_layer; }
@@ -42,22 +64,36 @@ namespace doc {
     Layer* layer() { return m_layer; }
     Cel* cel();
 
+    void focus(Focus focus) { m_focus = focus; }
     void document(Document* document) { m_document = document; }
     void sprite(Sprite* sprite) { m_sprite = sprite; }
     void layer(Layer* layer) { m_layer = layer; }
     void frame(frame_t frame) { m_frame = frame; }
 
-    LayerIndex layerIndex() const;
-    void layerIndex(LayerIndex layerIndex);
+    const SelectedLayers& selectedLayers() const { return m_selectedLayers; }
+    SelectedLayers& selectedLayers() { return m_selectedLayers; }
+    void selectedLayers(const SelectedLayers& selectedLayers) {
+      m_selectedLayers = selectedLayers;
+    }
+
+    const SelectedFrames& selectedFrames() const { return m_selectedFrames; }
+    SelectedFrames& selectedFrames() { return m_selectedFrames; }
+    void selectedFrames(const SelectedFrames& selectedFrames) {
+      m_selectedFrames = selectedFrames;
+    }
+
     Palette* palette();
     Image* image(int* x = nullptr, int* y = nullptr, int* opacity = nullptr) const;
     Palette* palette() const;
 
   private:
+    Focus m_focus;
     Document* m_document;
     Sprite* m_sprite;
     Layer* m_layer;
     frame_t m_frame;
+    SelectedLayers m_selectedLayers;
+    SelectedFrames m_selectedFrames;
   };
 
 } // namespace app
diff --git a/src/doc/sprite.cpp b/src/doc/sprite.cpp
index 391ef51f5..00e8718f8 100644
--- a/src/doc/sprite.cpp
+++ b/src/doc/sprite.cpp
@@ -19,7 +19,6 @@
 #include "doc/frame_tag.h"
 #include "doc/image_impl.h"
 #include "doc/layer.h"
-#include "doc/layers_range.h"
 #include "doc/palette.h"
 #include "doc/primitives.h"
 #include "doc/remap.h"
@@ -30,9 +29,6 @@
 
 namespace doc {
 
-static Layer* index2layer(const Layer* layer, const LayerIndex& index, int* index_count);
-static LayerIndex layer2index(const Layer* layer, const Layer* find_layer, int* index_count);
-
 //////////////////////////////////////////////////////////////////////
 // Constructors/Destructor
 
@@ -47,7 +43,7 @@ Sprite::Sprite(PixelFormat format, int width, int height, int ncolors)
   ASSERT(width > 0 && height > 0);
 
   m_frlens.push_back(100);      // First frame with 100 msecs of duration
-  m_folder = new LayerFolder(this);
+  m_root = new LayerGroup(this);
 
   // Generate palette
   switch (format) {
@@ -84,7 +80,7 @@ Sprite::Sprite(const ImageSpec& spec, int ncolors)
 Sprite::~Sprite()
 {
   // Destroy layers
-  delete m_folder;
+  delete m_root;
 
   // Destroy palettes
   {
@@ -125,7 +121,7 @@ Sprite* Sprite::createBasicSprite(doc::PixelFormat format, int width, int height
     }
 
     // Add the layer in the sprite.
-    sprite->folder()->addLayer(layer.release()); // Release the layer because it's owned by the sprite
+    sprite->root()->addLayer(layer.release()); // Release the layer because it's owned by the sprite
   }
 
   return sprite.release();
@@ -200,15 +196,10 @@ int Sprite::getMemSize() const
 //////////////////////////////////////////////////////////////////////
 // Layers
 
-LayerFolder* Sprite::folder() const
-{
-  return m_folder;
-}
-
 LayerImage* Sprite::backgroundLayer() const
 {
-  if (folder()->getLayersCount() > 0) {
-    Layer* bglayer = *folder()->getLayerBegin();
+  if (root()->layersCount() > 0) {
+    Layer* bglayer = root()->layers().front();
 
     if (bglayer->isBackground()) {
       ASSERT(bglayer->isImage());
@@ -218,50 +209,17 @@ LayerImage* Sprite::backgroundLayer() const
   return NULL;
 }
 
-LayerIndex Sprite::countLayers() const
+Layer* Sprite::firstBrowsableLayer() const
 {
-  return LayerIndex(folder()->getLayersCount());
+  Layer* layer = root()->firstLayer();
+  while (layer->isBrowsable())
+    layer = static_cast<LayerGroup*>(layer)->firstLayer();
+  return layer;
 }
 
-LayerIndex Sprite::firstLayer() const
+layer_t Sprite::allLayersCount() const
 {
-  return LayerIndex(0);
-}
-
-LayerIndex Sprite::lastLayer() const
-{
-  return LayerIndex(folder()->getLayersCount()-1);
-}
-
-Layer* Sprite::layer(int layerIndex) const
-{
-  return indexToLayer(LayerIndex(layerIndex));
-}
-
-Layer* Sprite::indexToLayer(LayerIndex index) const
-{
-  if (index < LayerIndex(0))
-    return NULL;
-
-  int index_count = -1;
-  return index2layer(folder(), index, &index_count);
-}
-
-LayerIndex Sprite::layerToIndex(const Layer* layer) const
-{
-  int index_count = -1;
-  return layer2index(folder(), layer, &index_count);
-}
-
-void Sprite::getLayersList(std::vector<Layer*>& layers) const
-{
-  // TODO support subfolders
-  LayerConstIterator it = m_folder->getLayerBegin();
-  LayerConstIterator end = m_folder->getLayerEnd();
-
-  for (; it != end; ++it) {
-    layers.push_back(*it);
-  }
+  return root()->allLayersCount();
 }
 
 //////////////////////////////////////////////////////////////////////
@@ -383,12 +341,12 @@ void Sprite::addFrame(frame_t newFrame)
   for (frame_t i=m_frames-1; i>=newFrame; --i)
     setFrameDuration(i, frameDuration(i-1));
 
-  folder()->displaceFrames(newFrame, +1);
+  root()->displaceFrames(newFrame, +1);
 }
 
 void Sprite::removeFrame(frame_t frame)
 {
-  folder()->displaceFrames(frame, -1);
+  root()->displaceFrames(frame, -1);
 
   frame_t newTotal = m_frames-1;
   for (frame_t i=frame; i<newTotal; ++i)
@@ -493,12 +451,11 @@ void Sprite::remapImages(frame_t frameFrom, frame_t frameTo, const Remap& remap)
 
 void Sprite::pickCels(int x, int y, frame_t frame, int opacityThreshold, CelList& cels) const
 {
-  std::vector<Layer*> layers;
-  getLayersList(layers);
+  LayerList layers = allVisibleLayers();
 
   for (int i=(int)layers.size()-1; i>=0; --i) {
     Layer* layer = layers[i];
-    if (!layer->isImage() || !layer->isVisible())
+    if (!layer->isImage())
       continue;
 
     Cel* cel = layer->cel(frame);
@@ -541,77 +498,51 @@ void Sprite::pickCels(int x, int y, frame_t frame, int opacityThreshold, CelList
 //////////////////////////////////////////////////////////////////////
 // Iterators
 
-LayersRange Sprite::layers() const
+LayerList Sprite::allLayers() const
 {
-  return LayersRange(this, LayerIndex(0), LayerIndex(countLayers()-1));
+  LayerList list;
+  m_root->allLayers(list);
+  return list;
+}
+
+LayerList Sprite::allVisibleLayers() const
+{
+  LayerList list;
+  m_root->allVisibleLayers(list);
+  return list;
+}
+
+LayerList Sprite::allBrowsableLayers() const
+{
+  LayerList list;
+  m_root->allBrowsableLayers(list);
+  return list;
 }
 
 CelsRange Sprite::cels() const
 {
-  return CelsRange(this, frame_t(0), lastFrame());
+  SelectedFrames selFrames;
+  selFrames.insert(0, lastFrame());
+  return CelsRange(this, selFrames);
 }
 
 CelsRange Sprite::cels(frame_t frame) const
 {
-  return CelsRange(this, frame, frame);
+  SelectedFrames selFrames;
+  selFrames.insert(frame);
+  return CelsRange(this, selFrames);
 }
 
 CelsRange Sprite::uniqueCels() const
 {
-  return CelsRange(this, frame_t(0), lastFrame(), CelsRange::UNIQUE);
+  SelectedFrames selFrames;
+  selFrames.insert(0, lastFrame());
+  return CelsRange(this, selFrames, CelsRange::UNIQUE);
 }
 
-CelsRange Sprite::uniqueCels(frame_t from, frame_t to) const
+CelsRange Sprite::uniqueCels(const SelectedFrames& selFrames) const
 {
-  return CelsRange(this, from, to, CelsRange::UNIQUE);
-}
-
-//////////////////////////////////////////////////////////////////////
-
-static Layer* index2layer(const Layer* layer, const LayerIndex& index, int* index_count)
-{
-  if (index == *index_count)
-    return (Layer*)layer;
-  else {
-    (*index_count)++;
-
-    if (layer->isFolder()) {
-      Layer *found;
-
-      LayerConstIterator it = static_cast<const LayerFolder*>(layer)->getLayerBegin();
-      LayerConstIterator end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it) {
-        if ((found = index2layer(*it, index, index_count)))
-          return found;
-      }
-    }
-
-    return NULL;
-  }
-}
-
-static LayerIndex layer2index(const Layer* layer, const Layer* find_layer, int* index_count)
-{
-  if (layer == find_layer)
-    return LayerIndex(*index_count);
-  else {
-    (*index_count)++;
-
-    if (layer->isFolder()) {
-      int found;
-
-      LayerConstIterator it = static_cast<const LayerFolder*>(layer)->getLayerBegin();
-      LayerConstIterator end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it) {
-        if ((found = layer2index(*it, find_layer, index_count)) >= 0)
-          return LayerIndex(found);
-      }
-    }
-
-    return LayerIndex(-1);
-  }
+  return CelsRange(this, selFrames, CelsRange::UNIQUE);
 }
 
 } // namespace doc
diff --git a/src/doc/sprite.h b/src/doc/sprite.h
index 59f340919..fd1428ba7 100644
--- a/src/doc/sprite.h
+++ b/src/doc/sprite.h
@@ -16,7 +16,6 @@
 #include "doc/frame_tags.h"
 #include "doc/image_ref.h"
 #include "doc/image_spec.h"
-#include "doc/layer_index.h"
 #include "doc/object.h"
 #include "doc/pixel_format.h"
 #include "doc/pixel_ratio.h"
@@ -31,13 +30,13 @@ namespace doc {
   class Document;
   class Image;
   class Layer;
-  class LayerFolder;
+  class LayerGroup;
   class LayerImage;
-  class LayersRange;
   class Mask;
   class Palette;
   class Remap;
   class RgbMap;
+  class SelectedFrames;
 
   typedef std::vector<Palette*> PalettesList;
 
@@ -90,18 +89,10 @@ namespace doc {
     ////////////////////////////////////////
     // Layers
 
-    LayerFolder* folder() const;
+    LayerGroup* root() const { return m_root; }
     LayerImage* backgroundLayer() const;
-
-    LayerIndex countLayers() const;
-    LayerIndex firstLayer() const;
-    LayerIndex lastLayer() const;
-
-    Layer* layer(int layerIndex) const;
-    Layer* indexToLayer(LayerIndex index) const;
-    LayerIndex layerToIndex(const Layer* layer) const;
-
-    void getLayersList(std::vector<Layer*>& layers) const;
+    Layer* firstBrowsableLayer() const;
+    layer_t allLayersCount() const;
 
     ////////////////////////////////////////
     // Palettes
@@ -154,11 +145,14 @@ namespace doc {
     ////////////////////////////////////////
     // Iterators
 
-    LayersRange layers() const;
+    LayerList allLayers() const;
+    LayerList allVisibleLayers() const;
+    LayerList allBrowsableLayers() const;
+
     CelsRange cels() const;
     CelsRange cels(frame_t frame) const;
     CelsRange uniqueCels() const;
-    CelsRange uniqueCels(frame_t from, frame_t to) const;
+    CelsRange uniqueCels(const SelectedFrames& selFrames) const;
 
   private:
     Document* m_document;
@@ -167,7 +161,7 @@ namespace doc {
     frame_t m_frames;                      // how many frames has this sprite
     std::vector<int> m_frlens;             // duration per frame
     PalettesList m_palettes;               // list of palettes
-    LayerFolder* m_folder;                 // main folder of layers
+    LayerGroup* m_root;                    // main group of layers
 
     // Current rgb map
     mutable RgbMap* m_rgbMap;
diff --git a/src/doc/sprite_position.h b/src/doc/sprite_position.h
index 61893d29b..153d00553 100644
--- a/src/doc/sprite_position.h
+++ b/src/doc/sprite_position.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -9,34 +9,45 @@
 #pragma once
 
 #include "doc/frame.h"
-#include "doc/layer_index.h"
+#include "doc/layer.h"
+#include "doc/object.h"
+#include "doc/object_id.h"
 
 namespace doc {
 
-  class Sprite;
-
   class SpritePosition {
   public:
     SpritePosition()
-      : m_layerIndex(0)
+      : m_layerId(NullId)
       , m_frame(0) {
     }
-    SpritePosition(LayerIndex layerIndex, frame_t frame)
-      : m_layerIndex(layerIndex)
+
+    SpritePosition(const Layer* layer, frame_t frame)
+      : m_layerId(layer ? layer->id(): NullId)
       , m_frame(frame) {
     }
 
-    const LayerIndex& layerIndex() const { return m_layerIndex; }
-    const frame_t& frame() const { return m_frame; }
+    Layer* layer() const { return get<Layer>(m_layerId); }
+    ObjectId layerId() const { return m_layerId; }
+    frame_t frame() const { return m_frame; }
 
-    void layerIndex(LayerIndex layerIndex) { m_layerIndex = layerIndex; }
-    void frame(frame_t frame) { m_frame = frame; }
+    void layer(Layer* layer) {
+      m_layerId = (layer ? layer->id(): NullId);
+    }
 
-    bool operator==(const SpritePosition& o) const { return m_layerIndex == o.m_layerIndex && m_frame == o.m_frame; }
-    bool operator!=(const SpritePosition& o) const { return m_layerIndex != o.m_layerIndex || m_frame != o.m_frame; }
+    void layerId(ObjectId layerId) {
+      m_layerId = layerId;
+    }
+
+    void frame(frame_t frame) {
+      m_frame = frame;
+    }
+
+    bool operator==(const SpritePosition& o) const { return m_layerId == o.m_layerId && m_frame == o.m_frame; }
+    bool operator!=(const SpritePosition& o) const { return m_layerId != o.m_layerId || m_frame != o.m_frame; }
 
   private:
-    LayerIndex m_layerIndex;
+    ObjectId m_layerId;
     frame_t m_frame;
   };
 
diff --git a/src/doc/sprite_tests.cpp b/src/doc/sprite_tests.cpp
index 33da90405..e741ccf97 100644
--- a/src/doc/sprite_tests.cpp
+++ b/src/doc/sprite_tests.cpp
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -18,8 +18,75 @@
 
 using namespace doc;
 
-// lay1 = A _ B
-// lay2 = C D E
+TEST(Sprite, Layers)
+{
+  Sprite* spr = new Sprite(IMAGE_RGB, 32, 32, 256);
+
+  LayerImage* lay1 = new LayerImage(spr);
+  LayerImage* lay2 = new LayerImage(spr);
+  LayerImage* lay3 = new LayerImage(spr);
+  LayerImage* lay4 = new LayerImage(spr);
+  LayerImage* lay5 = new LayerImage(spr);
+  LayerImage* lay6 = new LayerImage(spr);
+  LayerImage* lay7 = new LayerImage(spr);
+  LayerGroup* grp1 = new LayerGroup(spr);
+  LayerGroup* grp2 = new LayerGroup(spr);
+  LayerGroup* grp3 = new LayerGroup(spr);
+
+  grp1->setVisible(false);
+  lay5->setVisible(false);
+  grp2->setCollapsed(true);
+
+  ;; grp2->addLayer(lay5);
+  ;;;; grp3->addLayer(lay7);
+  ;;;; grp3->addLayer(lay6);
+  ;; grp2->addLayer(grp3);
+  spr->root()->addLayer(grp2);
+  spr->root()->addLayer(lay2);
+  ;; grp1->addLayer(lay4);
+  ;; grp1->addLayer(lay3);
+  spr->root()->addLayer(grp1);
+  spr->root()->addLayer(lay1);
+
+  auto all = spr->allLayers();
+  ASSERT_EQ(10, all.size());
+  EXPECT_EQ(lay5, all[0]);
+  EXPECT_EQ(lay7, all[1]);
+  EXPECT_EQ(lay6, all[2]);
+  EXPECT_EQ(grp3, all[3]);
+  EXPECT_EQ(grp2, all[4]);
+  EXPECT_EQ(lay2, all[5]);
+  EXPECT_EQ(lay4, all[6]);
+  EXPECT_EQ(lay3, all[7]);
+  EXPECT_EQ(grp1, all[8]);
+  EXPECT_EQ(lay1, all[9]);
+
+  auto vis = spr->allVisibleLayers();
+  ASSERT_EQ(6, vis.size());
+  EXPECT_EQ(lay7, vis[0]);
+  EXPECT_EQ(lay6, vis[1]);
+  EXPECT_EQ(grp3, vis[2]);
+  EXPECT_EQ(grp2, vis[3]);
+  EXPECT_EQ(lay2, vis[4]);
+  EXPECT_EQ(lay1, vis[5]);
+
+  auto bro = spr->allBrowsableLayers();
+  ASSERT_EQ(6, bro.size());
+  EXPECT_EQ(grp2, bro[0]);
+  EXPECT_EQ(lay2, bro[1]);
+  EXPECT_EQ(lay4, bro[2]);
+  EXPECT_EQ(lay3, bro[3]);
+  EXPECT_EQ(grp1, bro[4]);
+  EXPECT_EQ(lay1, bro[5]);
+}
+
+//            frames
+//            0 1 2
+// root
+// - lay1:    A~~~B
+// - lay2:    C D~E
+// - grp1:
+//   - lay3:  F G~H
 TEST(Sprite, CelsRange)
 {
   Sprite* spr = new Sprite(IMAGE_RGB, 32, 32, 256);
@@ -27,8 +94,12 @@ TEST(Sprite, CelsRange)
 
   LayerImage* lay1 = new LayerImage(spr);
   LayerImage* lay2 = new LayerImage(spr);
-  spr->folder()->addLayer(lay1);
-  spr->folder()->addLayer(lay2);
+  LayerGroup* grp1 = new LayerGroup(spr);
+  LayerImage* lay3 = new LayerImage(spr);
+  spr->root()->addLayer(lay1);
+  spr->root()->addLayer(lay2);
+  spr->root()->addLayer(grp1);
+  grp1->addLayer(lay3);
 
   ImageRef imgA(Image::create(IMAGE_RGB, 32, 32));
   Cel* celA = new Cel(frame_t(0), imgA);
@@ -47,6 +118,16 @@ TEST(Sprite, CelsRange)
   lay2->addCel(celD);
   lay2->addCel(celE);
 
+  ImageRef imgF(Image::create(IMAGE_RGB, 32, 32));
+  ImageRef imgG(Image::create(IMAGE_RGB, 32, 32));
+  Cel* celF = new Cel(frame_t(0), imgF);
+  Cel* celG = new Cel(frame_t(1), imgG);
+  Cel* celH = Cel::createLink(celG);
+  celH->setFrame(frame_t(2));
+  lay3->addCel(celF);
+  lay3->addCel(celG);
+  lay3->addCel(celH);
+
   int i = 0;
   for (Cel* cel : spr->cels()) {
     switch (i) {
@@ -55,10 +136,13 @@ TEST(Sprite, CelsRange)
       case 2: EXPECT_EQ(cel, celC); break;
       case 3: EXPECT_EQ(cel, celD); break;
       case 4: EXPECT_EQ(cel, celE); break;
+      case 5: EXPECT_EQ(cel, celF); break;
+      case 6: EXPECT_EQ(cel, celG); break;
+      case 7: EXPECT_EQ(cel, celH); break;
     }
     ++i;
   }
-  EXPECT_EQ(5, i);
+  EXPECT_EQ(8, i);
 
   i = 0;
   for (Cel* cel : spr->uniqueCels()) {
@@ -66,39 +150,44 @@ TEST(Sprite, CelsRange)
       case 0: EXPECT_EQ(cel, celA); break;
       case 1: EXPECT_EQ(cel, celC); break;
       case 2: EXPECT_EQ(cel, celD); break;
+      case 3: EXPECT_EQ(cel, celF); break;
+      case 4: EXPECT_EQ(cel, celG); break;
     }
     ++i;
   }
-  EXPECT_EQ(3, i);
+  EXPECT_EQ(5, i);
 
   i = 0;
   for (Cel* cel : spr->cels(frame_t(0))) {
     switch (i) {
       case 0: EXPECT_EQ(cel, celA); break;
       case 1: EXPECT_EQ(cel, celC); break;
+      case 2: EXPECT_EQ(cel, celF); break;
     }
     ++i;
   }
-  EXPECT_EQ(2, i);
+  EXPECT_EQ(3, i);
 
   i = 0;
   for (Cel* cel : spr->cels(frame_t(1))) {
     switch (i) {
       case 0: EXPECT_EQ(cel, celD); break;
+      case 1: EXPECT_EQ(cel, celG); break;
     }
     ++i;
   }
-  EXPECT_EQ(1, i);
+  EXPECT_EQ(2, i);
 
   i = 0;
   for (Cel* cel : spr->cels(frame_t(2))) {
     switch (i) {
       case 0: EXPECT_EQ(cel, celB); break;
       case 1: EXPECT_EQ(cel, celE); break;
+      case 2: EXPECT_EQ(cel, celH); break;
     }
     ++i;
   }
-  EXPECT_EQ(2, i);
+  EXPECT_EQ(3, i);
 }
 
 int main(int argc, char** argv)
diff --git a/src/doc/test_context.h b/src/doc/test_context.h
index 9b8e1bb30..9a676a1f7 100644
--- a/src/doc/test_context.h
+++ b/src/doc/test_context.h
@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2015 David Capello
+// Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -31,7 +31,7 @@ namespace doc {
 
       site->document(doc);
       site->sprite(doc->sprite());
-      site->layer(doc->sprite()->folder()->getFirstLayer());
+      site->layer(doc->sprite()->root()->firstLayer());
       site->frame(0);
     }
 
diff --git a/src/render/quantization.cpp b/src/render/quantization.cpp
index 9c7787d47..aa4299f28 100644
--- a/src/render/quantization.cpp
+++ b/src/render/quantization.cpp
@@ -71,7 +71,7 @@ Palette* create_palette_from_sprite(
     palette,
     // Transparent color is needed if we have transparent layers
     (sprite->backgroundLayer() &&
-     sprite->countLayers() == 1 ? -1: sprite->transparentColor()),
+     sprite->allLayersCount() == 1 ? -1: sprite->transparentColor()),
     delegate);
 
   return palette;
diff --git a/src/render/render.cpp b/src/render/render.cpp
index 6e479140d..f31dca928 100644
--- a/src/render/render.cpp
+++ b/src/render/render.cpp
@@ -689,7 +689,7 @@ void Render::renderSprite(
   // Draw the background layer.
   m_globalOpacity = 255;
   renderLayer(
-    m_sprite->folder(), dstImage,
+    m_sprite->root(), dstImage,
     area, frame, compositeImage,
     true,
     false,
@@ -702,7 +702,7 @@ void Render::renderSprite(
   // Draw the transparent layers.
   m_globalOpacity = 255;
   renderLayer(
-    m_sprite->folder(), dstImage,
+    m_sprite->root(), dstImage,
     area, frame, compositeImage,
     false,
     true,
@@ -740,7 +740,7 @@ void Render::renderOnionskin(
   if (m_onionskin.type() != OnionskinType::NONE) {
     FrameTag* loop = m_onionskin.loopTag();
     Layer* onionLayer = (m_onionskin.layer() ? m_onionskin.layer():
-                                               m_sprite->folder());
+                                               m_sprite->root());
     frame_t frameIn;
 
     for (frame_t frameOut = frame - m_onionskin.prevFrames();
@@ -970,13 +970,10 @@ void Render::renderLayer(
       break;
     }
 
-    case ObjectType::LayerFolder: {
-      LayerConstIterator it = static_cast<const LayerFolder*>(layer)->getLayerBegin();
-      LayerConstIterator end = static_cast<const LayerFolder*>(layer)->getLayerEnd();
-
-      for (; it != end; ++it) {
+    case ObjectType::LayerGroup: {
+      for (const Layer* child : static_cast<const LayerGroup*>(layer)->layers()) {
         renderLayer(
-          *it, image,
+          child, image,
           area, frame,
           compositeImage,
           render_background,
diff --git a/src/render/render_tests.cpp b/src/render/render_tests.cpp
index 42d8f3a80..94345802c 100644
--- a/src/render/render_tests.cpp
+++ b/src/render/render_tests.cpp
@@ -68,7 +68,7 @@ TEST(Render, Basic)
   Context ctx;
   Document* doc = ctx.documents().add(2, 2, ColorMode::RGB);
 
-  Image* src = doc->sprite()->layer(0)->cel(0)->image();
+  Image* src = doc->sprite()->root()->firstLayer()->cel(0)->image();
   clear_image(src, 2);
 
   base::UniquePtr<Image> dst(Image::create(IMAGE_RGB, 2, 2));
@@ -88,8 +88,8 @@ TYPED_TEST(RenderAllModes, CheckDefaultBackgroundMode)
   Document* doc = ctx.documents().add(2, 2,
     ColorMode(ImageTraits::pixel_format));
 
-  EXPECT_TRUE(!doc->sprite()->layer(0)->isBackground());
-  Image* src = doc->sprite()->layer(0)->cel(0)->image();
+  EXPECT_TRUE(!doc->sprite()->root()->firstLayer()->isBackground());
+  Image* src = doc->sprite()->root()->firstLayer()->cel(0)->image();
   clear_image(src, 0);
   put_pixel(src, 1, 1, 1);
 
@@ -109,8 +109,8 @@ TEST(Render, DefaultBackgroundModeWithNonzeroTransparentIndex)
   Document* doc = ctx.documents().add(2, 2, ColorMode::INDEXED);
   doc->sprite()->setTransparentColor(2); // Transparent color is index 2
 
-  EXPECT_TRUE(!doc->sprite()->layer(0)->isBackground());
-  Image* src = doc->sprite()->layer(0)->cel(0)->image();
+  EXPECT_TRUE(!doc->sprite()->root()->firstLayer()->isBackground());
+  Image* src = doc->sprite()->root()->firstLayer()->cel(0)->image();
   clear_image(src, 2);
   put_pixel(src, 1, 1, 1);
 
@@ -188,7 +188,7 @@ TEST(Render, ZoomAndDstBounds)
   // 0 4 4
   // 0 4 4
   Document* doc = ctx.documents().add(3, 3, ColorMode::RGB);
-  Image* src = doc->sprite()->layer(0)->cel(0)->image();
+  Image* src = doc->sprite()->root()->firstLayer()->cel(0)->image();
   clear_image(src, 0);
   fill_rect(src, 1, 1, 2, 2, 4);