When can I use... : Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers.
Mobile HTML5 compatibility : HTML5 compatibility on mobile and tablet browsers with testing on real devices
Email Standards Project : The Email Standards Project is about working with email client developers and the design community to improve web standards support and accessibility ...
Explorer Exposed! : These CSS bugs are all found only in Internet Explorer, versions 5 and higher. To see the demos properly, they must be viewed in IE, of course.
Introduction to WAI ARIA : This article is for those who are new to ARIA. You need an understanding of HTML and the potential difficulties that people with disabilities can face...
HTML: The Living Standard. A technical specification for Web developers.