fmt/doc/bootstrap/searchbox.html

{%- if pagename != "search" %}
<form action="{{ pathto('search') }}" method="get">
 <div class="form-group">
  <input type="text" name="q" class="form-control" placeholder="Search" />
 </div>
  <input type="hidden" name="check_keywords" value="yes" />
  <input type="hidden" name="area" value="default" />
</form>
{%- endif %}