code: def _subscribe_broadcast(self, sub_id, channel, callback, **kwargs):
          
          headers = {}
          if kwargs.get("ignore_namespace"):
              destination = "/topic/" + channel
          else:
              destination = "/topic/" + self._namespace + channel
          if kwargs.get("retroactive"):
              headers["activemq.retroactive"] = "true"
          if kwargs.get("transformation"):
              if kwargs["transformation"] == True:
                  headers["transformation"] = "jms-object-json"
              else:
                  headers["transformation"] = kwargs["transformation"]
          self._conn.subscribe(destination, sub_id, headers=headers)
docs: Listen to a broadcast topic, notify via callback function.
          :param sub_id: ID for this subscription in the transport layer
          :param channel: Topic name to subscribe to
          :param callback: Function to be called when messages are received
          :param **kwargs: Further parameters for the transport layer. For example
            ignore_namespace: Do not apply namespace to the destination name
            retroactive:      Ask broker to send old messages if possible
            transformation:   Transform messages into different format. If set
                              to True, will use 'jms-object-json' formatting.