geSortByTabIndex(left, right);
      },

      /**
       * Merge sort iterator, merges the two arrays into one, sorted by tab index.
       * @param {!Array<!HTMLElement>} left
       * @param {!Array<!HTMLElement>} right
       * @return {!Array<!HTMLElement>}
       * @private
       */
      _mergeSortByTabIndex: function(left, right) {
        var result = [];
        while ((left.length > 0) && (right.length > 0)) {
          if (this._hasLowerTabOrder(left[0], right[0])) {
            result.push(rig