
        if (this.isFocusable(element)) {
          var tabIndex = element.getAttribute('tabindex') || 0;
          return Number(tabIndex);
        }
        return -1;
      },

      /**
       * Searches for nodes that are tabbable and adds them to the `result` array.
       * Returns if the `result` array needs to be sorted by tabindex.
       * @param {!Node} node The starting point for the search; added to `result`
       * if tabbable.
       * @param {!Array<!HTMLElement>} result
       * @return {