code: protected function fetchQueue(string $eventName): SplPriorityQueue
      {
          if (isset($this->events[$eventName]) == false) {
              $this->events[$eventName] = $this->createQueue();
          }
  
          return $this->events[$eventName];
      }
docs: Fetches a priority events queue by event type.
  
  @param  string $eventName
  @return SplPriorityQueue