code: function($item, preventScroll) {
              if (!this.settings.multi) {
                  return this.selectItem($item, true);
              }
  
              this.deselectAll();
  
              this.$last = $item;
              this.last = this.getItemIndex($item);
  
              this.setFocusableItem($item);
              this.focusItem($item, preventScroll);
  
              // prepare params for $.slice()
              var sliceFrom, sliceTo;
  
              if (this.first < this.last) {
                  sliceFrom = this.first;
                  sliceTo = this.last + 1;
              }
              else {
                  sliceFrom = this.last;
                  sliceTo = this.first + 1;
              }
  
              this._selectItems(this.$items.slice(sliceFrom, sliceTo));
          }
docs: Select Range