code: @Override
      public void renderHead(final Component _component,
                             final IHeaderResponse _response)
      {
          super.renderHead(_component, _response);
          _response.render(JavaScriptHeaderItem.forScript(MessageListenerBehavior.getScript(_component),
                              _component.getClass().getName() + "_MessageListener"));
  
      }
docs: Render to the web response whatever the component wants to contribute to
  the head section.
  
  @param _component    Component this behavior belongs to
  @param _response     Response object