/**
  * Return default handler objects for supported tasks.
  * @param string $handler_type Specific functionality required.
  * @param OBJECT_RENDERER_OPTIONS $options
  * @return object
  * @access private
  */
 protected function _default_handler_for($handler_type, $options = null)
 {
     switch ($handler_type) {
         case Handler_print_renderer:
         case Handler_html_renderer:
         case Handler_text_renderer:
         case Handler_source_renderer:
             include_once 'webcore/gui/content_object_renderer.php';
             return new CONTENT_OBJECT_RENDERER($this->app, $options);
         case Handler_mail:
             include_once 'webcore/mail/content_object_mail_renderer.php';
             return new CONTENT_OBJECT_MAIL_RENDERER($this->app);
         case Handler_history_item:
             include_once 'webcore/obj/webcore_history_items.php';
             return new CONTENT_OBJECT_HISTORY_ITEM($this->app);
         default:
             return parent::_default_handler_for($handler_type, $options);
     }
 }