pocketmine\level\Level::getId PHP Method

    public final function getId() : int
    {
        return $this->levelId;
    }

 public function blockZone(Vector3 $a, Vector3 $b, Level $level)
 {
     if (!isset($this->activeZones[$level->getId()])) {
         $this->activeZones[$level->getId()] = [];
     }
     $id = count($this->activeZones[$level->getId()]);
     $this->activeZones[$level->getId()][$id] = [$a, $b];
     $this->clearZone($level, $id);
     return $id;
 }