code: function(start) {
          var itemsToShow = this.options.itemsToShow,
              length = this.items.length,
              stop = start + itemsToShow,
              set = $([]),
              tabs = this.tabs
                  .removeClass('is-active')
                  .aria('toggled', false);
  
          if (!tabs.length) {
              return;
          }
  
          if (this.options.infinite) {
              length = length - (itemsToShow * 2);
          }
  
          if (start >= 0) {
              set = set.add(tabs.slice(start, stop));
          } else {
              set = set.add(tabs.slice(0, stop));
              set = set.add(tabs.slice(start));
          }
  
          if (stop > length) {
              set = set.add(tabs.slice(0, stop - length));
          }
  
          set
              .addClass('is-active')
              .aria('toggled', true);
      }
docs: Update the active state for the tab indicators.
  
  @param {Number} start
  @private