code: @Nonnull
    public static <IMPLTYPE extends IHCElementWithChildren <?>> IMPLTYPE makeDropdownToggle (@Nonnull final IMPLTYPE aElement)
    {
      aElement.addClass (CBootstrapCSS.DROPDOWN_TOGGLE).addChild (new BootstrapCaret ());
      aElement.customAttrs ().setDataAttr ("toggle", "dropdown");
      aElement.customAttrs ().setAriaHasPopup (true);
      aElement.customAttrs ().setAriaExpanded (false);
      return aElement;
    }
docs: Call this method to convert an element to a dropdown toggle. Important:
  call this after all children are added, because a caret is added at the
  end!
  
  @param aElement
  The element to use. May not be <code>null</code>.
  @param <IMPLTYPE>
  Implementation type
  @return The passed element. Never <code>null</code>.