def add(self, handler, allow_dupe=False, send_event=True):
self._add(handler, allow_dupe=allow_dupe, send_event=send_event)<EOL>return handler<EOL>
Add handler instance and attach any events to it.

:param object handler: handler instance
:param bool allow_dupe: If True, allow registering a handler more than once.
:return object: The handler you added is given back so this can be used as a decorator.