public delegate void EventListener (Object obj)
A function which is called when an object emits a matching event, as used in add_focus_tracker.
Currently the only events for which object-specific handlers are supported are events of type "focus:". Most clients of ATK will prefer to attach signal handlers for the various ATK signals instead.
An Object instance for whom the callback will be called when the specified event (e.g. 'focus:') takes place.