whatwg living html 0.0 and w3c html 5.1 whatwg living html and w3c html 5.1 https://developers.whatwg.org https://html.spec.whatwg.org/multipage/ http://www.w3.org/html/wg/drafts/html/master/ see also http://dev.w3.org/html5/ https://validator.whatwg.org/ html standards validator w3c web