public function getRenderedValue()
 {
     if ($this->_contentSlot->render_function) {
         $renderFunction = $this->_contentSlot->render_function;
         if (method_exists($this->_content, $renderFunction)) {
             return $this->_content->{$renderFunction}($this);
         } else {
             if (method_exists($this->_contentSlot, $renderFunction)) {
                 return $this->_contentSlot->{$renderFunction}($this);
             } else {
                 sfSympalToolkit::autoloadHelper($renderFunction);
                 return $renderFunction($this->_content, $this->_contentSlot->name);
             }
         }
     } else {
         return $this->getRawValue();
     }
 }