+ rollbackTransaction: function() {
+ if(!this._currentTransaction) {
+ throw new Error('Transaction rollback requested, but there is no transaction in progress!');
+ }
+ this.replaceRoot(this._rollbackBackup);
+ this._rollbackBackup = null;
+ this._currentTransaction = null;
+ this._transformationLevel = 0;
+ },
+
+ transaction: function(callback, params) {