code: function(index) {
          this.items
              .removeClass('is-active')
              .aria('hidden', true)
              .slice(index, index + this.options.itemsToShow)
                  .addClass('is-active')
                  .aria('hidden', false);
      }
docs: Update the active state for the items while taking into account cloned elements.
  
  @param {Number} index
  @private