docs: function () {
          var args = Array.prototype.slice.call(arguments);
          var topic = args.splice(0, 1)[0];
          if (topic) {
              var list = listeners[topic];
              if (list) {
                  for (var i = list.length - 1; i >= 0; i--) {
                      var han = list[i], cb = han.cb;
                      if (cb) {
                          cb.apply(this, args);
                      }
                  }
              }
          }
      }