docs: def register_endpoint(self, endpoint, handler):
          """
          Register a handler for a message received from the Pebble.
  
          :param endpoint: The type of :class:`.PebblePacket` that is being listened for.
          :type endpoint: .PacketType
          :param handler: A callback to be called when a message is received.
          :type handler: callable
          :return: A handle that can be passed to :meth:`unregister_endpoint` to remove the handler.
          """
          return self.event_handler.register_handler((_EventType.Watch, endpoint), handler)