Don't make <h1><h1> nest

http://html5.org/tools/web-apps-tracker?from=925&to=926

In order to get the layout right, what is actually needed is a unit that  
acts like 'em' but ignores ancestor h1-h6 elements when calculating the  
computed style of font-size. Using 'rem' or similar isn't good enough  
because pages can set the font-size on root to something that isn't used  
for the actual text on the page, or some pages have a sidebar in a smaller  
font, etc.

So we've decided to do what webkit does. (Any element in between whose end  
tag isn't implied by <h1> makes them nest.)

-- 
Simon Pieters
Opera Software