code: function decorateElement(element) {
    const hasMissingTabIndex = Boolean(!element.getAttribute('tabindex') && element.tabIndex === -1);
  
    if (hasMissingTabIndex) {
      elementsWithMissingTabIndex.push(element);
      element.tabIndex = 0;
    }
  }
docs: Decorates element with tabindex attributes
  @param {HTMLElement} element
  @return {Object}
  @private