W3C cheatsheet
Content: Usability:
www.w3.org/2009/cheatsheet/ (xhtml-mp)
www.w3.org/2009/cheatsheet/ (xhtml-mp)
For web developers and designers, this mobile friendly reference from the W3C offers best practices lists for mobile, accessibility, internationalization and typography plus a searchable HTML, CSS, SVG, XPath property, element, attribute and function reference. It's a big (300+ KB) site and works best on advanced devices with JavaScript support. Source: W3C Blog