code: public void attach () {
  		if (target == null) return;
  		Array<EventListener> listeners = target.getListeners();
  		for (EventListener listener : listeners) {
  			if (listener instanceof TooltipInputListener) {
  				throw new IllegalStateException("More than one tooltip cannot be added to the same target!");
  			}
  		}
  
  		target.addListener(listener);
  	}
docs: Attaches tooltip to current target, must be called if tooltip listener was removed from target (for example by
  calling target.clearListeners() )