docs: function (items) {
              var data = this._data;
              var res = data.multipleSelect ? data.maxSelectedCount : 1;
              if (res == null) {
                  if (items == null) {
                      items = data.items;
                  }
                  res = 1 + items.length;
              }
              this.$assert(268, res >= 1);
              return res;
          }