docs: function(params, cb) {
      var correlationId = _cbt.put(offFetchResponse(cb));
      var msg = envelope(offFetch.encode(params.fetchFromCoordinator ? 1 : 0)
                                 .correlation(correlationId)
                                 .client(_options.clientId)
                                 .group(params.group)
                                 .topic(params.topic)
                                 .partition(params.partition)
                                 .end());
      sendMsg(msg, correlationId, cb);
    }