[whatwg] attribute value normalization

[Christoph Päper]

Anne van Kesteren:
> It appears that no browser has implemented the 'may' from HTML4

Confusingly (at least) Firefox 1.04 does trim tabulators and newlines, 
but not spaces, and only in HTML mode, not in XML mode.

<http://webdesign.crissov.de/temp/whatwg/attribute-normalization.html>
<http://webdesign.crissov.de/temp/whatwg/attribute-normalization.xhtml>

IE6 never trims.