Custom HTML Elements

Does anyone know of any big/important sites that use custom HTML elements i.e. ones that aren't in the spec?

>>13
HTML5 isn't a standard yet.

>>14
It's in proposal by the w3c which means it's most certainly to be the standard. The fact that it isn't official now doesn't mean it'll be any more of a standard when it is officially ratified.

>>15
http://www.w3.org/standards/techs/html#drafts
This document may not provide accurate information as the HTML 5 specification is still actively in development.

http://www.w3.org/TR/2012/WD-html5-20120329/
Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways.

>>17
The document says this disclaimer because that's the nature of working non-ratified standards. In practise, what are the chances that this specific feature will be changed before it is official? I'm will to bet that the chances are very low.

>>14
It's already been implemented by all the lastest browsers. That's all that really matters.

http://harmful.cat-v.org/standards/