code: private function orderObserversForPriority($a, $b) {
          if($a->order > $b->order) {
              return +1;
          } elseif ($a->order == $b->order) {
              return 0;
          }
          return -1;
      }
docs: Order The observers using the order integer value. Lower number is going
  to execute first, in case of have the same order it goes first the first
  observer assign to the event.
  
  @param stdClass $a
  @param stdClass $b
  @return int