/**
  * Sort the Messages by priority.
  */
 protected function sortMessagesByPriority(IPipeMessage $msgA, IPipeMessage $msgB)
 {
     if ($msgA->getPriority() == $msgB->getPriority()) {
         return 0;
     }
     return $msgA->getPriority() < $msgB->getPriority() ? -1 : 1;
 }