code: function(object, events, callback) {
        var listeners = this._listeners || (this._listeners = {});
        var id = object._listenerId || (object._listenerId = _.uniqueId('l'));
        listeners[id] = object;
        object.on(events, callback || this, this);
        return this;
      }
docs: An inversion-of-control version of `on`. Tell *this* object to listen to an event in another object ... keeping track of what it's listening to.