This method enables the event to bubble up the scene hierarchy so it will be
dispatched to the parent scene. For example, we have a parent scene and the parent
scene opens a child scene. In the child scene, we trigger an event and create an
event object (eventObj). Normally this event bubbles up until it reaches the root
box of the child scene and then stops. If any box reacts to the event and calls
eventObj.propagateScenes() when the event is bubbling up, then the event will be
dispatched to the parent scene after it bubbles to the root box of the child scene.
eventObj.propagateScenes();