Indicates whether the element is selected or not. This value is read-only. To change the selection, set either the selectedIndex or selectedItem property of the containing element.
Note that in multiprocess Firefox, this attribute means only that the user (or code) has initiated tab selection, not that the browser has actually switched to the tab. If your code needs to apply some styling to the currently selected tab, you should use the visuallyselected attribute, which is available from Firefox 40 onwards. See tab selection in multiprocess Firefox for more details.