code: function rollback(numVersions) {
              var snapshotsLength = this.$$snapshots ? this.$$snapshots.length : 0;
              numVersions = Math.min(numVersions || 1, snapshotsLength);
  
              if (numVersions < 0) {
                  numVersions = snapshotsLength;
              }
  
              if (snapshotsLength) {
                  this.rollbackTo(this.$$snapshots.length - numVersions);
              }
  
              return true;
          }
docs: Rolls back the resource to a previous snapshot.
  
  When numVersions is undefined or 0 then a single version is rolled back.
  When numVersions exceeds the stored number of snapshots then the resource is rolled back to the first snapshot version.
  When numVersions is less than 0 then the resource is rolled back to the first snapshot version.
  
  @param {Number|undefined} numVersions The number of versions to roll back to.  If undefined then
  @returns {Boolean} true if rollback was successful, false otherwise