Mobile HTML5 compatibility : HTML5 compatibility on mobile and tablet browsers with testing on real devices
HTML5 Please : Look up HTML5, CSS3, etc features, know if they are ready for use, and if so find out how you should use them – with polyfills, fallbacks or as they
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 ...
HTML: The Living Standard. A technical specification for Web developers.