code: function hasValidTabIndex(element) {
      if (!element.hasAttribute('tabindex') || element.tabIndex === undefined) {
          return false;
      }
      var /** @type {?} */ tabIndex = element.getAttribute('tabindex');
      // IE11 parses tabindex="" as the value "-32768"
      if (tabIndex == '-32768') {
          return false;
      }
      return !!(tabIndex && !isNaN(parseInt(tabIndex, 10)));
  }
docs: Gets whether an element has a valid tabindex.
  @param {?} element
  @return {?}