- handler A callable object to be invoked when the event
- is delivered to self. Pass None to disconnect an
- event handler.
+ :param source: Sometimes the event originates from a
+ different window than self, but you still
+ want to catch it in self. (For example, a
+ button event delivered to a frame.) By
+ passing the source of the event, the event
+ handling system is able to differentiate
+ between the same event type from different
+ controls.