Interface for classes capable of having callbacks to handle events.
|Handle an event, most often by executing the callbacks associated with the event.
|Return true if event handlers for the event propagation BubbleUp phase have been attached on this object.
|Returns true if event handlers, for the event propagation TrickleDown phase, are attached to this object.
|Adds an event handler to the instance. If the event handler has already been registered for the same phase (either TrickleDown or BubbleUp) then this method has no effect.
|Sends an event to the event handler.
|Remove callback from the instance.