code: function (el) {
              var carousel = this;
  
              if (el) {
                  if (carousel._focusableItemEl) {
                      carousel._focusableItemEl.tabIndex = -1;
                  }
                  carousel._focusableItemEl = el;
                  el.tabIndex = 0;
              }
          }
docs: Set the correct tab index for the Carousel items.
  
  @method _updateTabIndex
  @param el {Object} The element to be focussed
  @protected