code: public void setShowActionsBox(final boolean showActionsBox) {
          if (showActionsBox)
              attrMixin.setAttribute(ACTIONS_BOX, Boolean.toString(true));
          else
              attrMixin.removeAttribute(ACTIONS_BOX);
      }
docs: When set to <code>true</code>, adds two buttons to the top of
  the drop-down menu (<b>Select All</b> & <b>Deselect All</b>).<br>
  <br>
  Defaults to <code>false</code>.
  
  @param showActionsBox