code: function(models, options) {
        options = _.extend({}, options);
        var singular = !_.isArray(models);
        models = singular ? [models] : models.slice();
        var removed = this._removeModels(models, options);
        if (!options.silent && removed.length) {
          options.changes = {added: [], merged: [], removed: removed};
          this.trigger('update', this, options);
        }
        return singular ? removed[0] : removed;
      }
docs: Remove a model, or a list of models from the set.