docs: function (preEventExtender) {
      if (!preEventExtender || !_.isObject(preEventExtender)) {
        var err = new Error('Please inject a valid event extender object!');
        debug(err);
        throw err;
      }
      if (this.preEventExtenders.indexOf(preEventExtender) < 0) {
        preEventExtender.useCollection(this);
        this.preEventExtenders.push(preEventExtender);
      }
    }