* sorting the result by tabindex.
       * @param {!Node} node
       * @return {!Array<!HTMLElement>}
       */
      getTabbableNodes: function(node) {
        var result = [];
        // If there is at least one element with tabindex > 0, we need to sort
        // the final array by tabindex.
        var needsSortByTabIndex = this._collectTabbableNodes(node, result);
        if (needsSortByTabIndex) {
          return this._sortByTabIndex(result);
        }
        return result;
      },

      /**
   