def register_raw_outbound_handler(self, handler):
return self.event_handler.register_handler("<STR_LIT>", handler)<EOL>
Register a handler for all outgoing messages to be sent to the Pebble. Transport framing is not included.

:param handler: A callback to be called when any message is received.
:type handler: callable
:return: A handle that can be passed to :meth:`unregister_endpoint` to remove the handler.