idProperty

If you wish to find an actor by its id. There is no guarantee of uniqueness. Kyd itself doesn't use this field, it exists only because it might be useful. toString includes the id, which may help debugging.

You could use this for example, to give keys and locks and id. When you collect a key, look for all locks with the same id, and unlock them.

There are other ways (which may be better) to "find" an actor. For example, if I want my Director to find the player, I add a registerPlayer() method to Director, and call it from Behaviour.onEnteredStage or Behaviour.onActStarted.