protected function getModalFeedback($identifier)
 {
     foreach ($this->item->getModalFeedbacks() as $feedback) {
         if ($feedback->getIdentifier() == $identifier) {
             return $feedback;
         }
     }
     throw new ParsingException('cannot found the modal feedback with identifier ' . $identifier);
 }
 protected function getModalFeedbacks(Item $qtiItem)
 {
     $returnValue = array();
     $feedbacks = $qtiItem->getModalFeedbacks();
     foreach ($feedbacks as $feedback) {
         $returnValue[$feedback->getSerial()] = $feedback->toArray();
     }
     return $returnValue;
 }