protected function renderAttributes(Text_Renderer $renderer)
 {
     $html = parent::renderAttributes($renderer);
     // todo: sort the array by predefined order
     $events = $this->_events->toArray();
     foreach ($events as $key => $val) {
         if ($val !== null) {
             $this->renderEventAttribute($key, $val, $renderer);
         }
     }
 }