Official Google Webmaster Central Blog: Updating our technical Webmaster Guidelines
Google has updated its advice to people making websites, who might want to have those sites indexed by Google. There are two simple bits of advice: optimise for performance, and use progressive enhancement.
Just like modern browsers, our rendering engine might not support all of the technologies a page uses. Make sure your web design adheres to the principles of progressive enhancement as this helps our systems (and a wider range of browsers) see usable content and basic functionality when certain web design features are not yet supported.