code: def join(self, master):
          
          self.avTransport.SetAVTransportURI([
              ('InstanceID', 0),
              ('CurrentURI', 'x-rincon:{0}'.format(master.uid)),
              ('CurrentURIMetaData', '')
          ])
          self._zgs_cache.clear()
          self._parse_zone_group_state()
docs: Join this speaker to another "master" speaker.