code: public function insert($data, /*# int */ $priority = 0, $extra = null)
      {
          // fix priority
          $pri = $this->fixPriority((int) $priority);
  
          // generate key to be used (int)
          $key = $this->generateKey($pri);
  
          // make sure not duplicated
          $this->remove($data);
  
          // added to the queue
          $this->queue[$key] = [
              'data' => $data, 'priority' => $pri, 'extra' => $extra
          ];
  
          // mark as not sorted
          $this->sorted = false;
  
          return $this;
      }
docs: {@inheritDoc}
  
  @since  2.0.21 added extra data