code: function () {
                      if (this._lastGroup && typeof this._lastGroup.index === "number") {
                          return Promise.wrap(this._count);
                      } else {
                          // Even if there's a current estimate for _count, consider this call to be a request to determine the true
                          // count.
  
                          var that = this;
                          var countPromise = new Promise(function (complete) {
                              var fetch = {
                                  initialBatch: function () {
                                      that._fetchNextIndex();
                                  },
                                  getGroup: function () { return null; },
                                  countBefore: 0,
                                  countAfter: 0,
                                  complete: function (failed) {
                                      if (failed) {
                                          that._count = 0;
                                      }
  
                                      var count = that._count;
                                      if (typeof count === "number") {
                                          complete(count);
                                          return true;
                                      } else {
                                          return false;
                                      }
                                  }
                              };
  
                              that._fetchQueue.push(fetch);
  
                              if (!that._itemBatch) {
                                  that._continueFetch(fetch);
                              }
                          });
  
                          return (typeof this._count === "number" ? Promise.wrap(this._count) : countPromise);
                      }
                  }
docs: itemsFromDescription: not implemented