Tell #ClutterGestureAction that it needs to wait until the drag threshold has been exceeded before considering that the gesture has begun;
Tell #ClutterGestureAction that the gesture must begin immediately and that it must be cancelled once the drag exceed the configured threshold.
Tell #ClutterGestureAction that the gesture must begin immediately and there's no drag limit that will cause its cancellation;
Enum passed to the clutter_gesture_action_set_threshold_trigger_edge() function.