http://www.w3.org/QA/2009/11/w3c_cheatsheet_for_developers.html

“This cheatsheet aims at providing in a very compact and mobile-friendly format a compilation of useful knowledge extracted from W3C specifications — at this time, CSS, HTML, SVG and XPath —, completed by summaries of guidelines developed at W3C, in particular the WCAG2 accessibility guidelines, the Mobile Web Best Practices, and a number of internationalization tips.

Its main feature is a lookup search box, where one can start typing a keyword and get a list of matching
properties/elements/attributes/functions in the above-mentioned specifications, and further details on those when selecting the one of interest.”