docs: function mergeListeners(emitter) {
        var events = emitter._events;
        _.each(events, function (fns, type) {
          if (Array.isArray(fns)) {
            _.each(fns, function (fn) {
              if (_.isFunction(fn)) {
                self.on(type, fn);
              }
            });
          } else if (_.isFunction(fns)) {
            self.on(type, fns);
          }
        });
      }