code: function(models, options) {
        if (_.isArray(models)) {
          for (var i = 0, l = models.length; i < l; i++) {
            this._add(models[i], options);
          }
        } else {
          this._add(models, options);
        }
        return this;
      }
docs: Add a model, or list of models to the set. Pass **silent** to avoid firing the `added` event for every new model.