[whatwg] classList should perhaps move from HTMLElement to Element

[Cameron McCormack]

Rik Cabanier:
> Who would do this in the current SVG world? As you say, (!elt.className)
> would always return false...
> Are you worried that new content won't work with an old viewer?

No that would actually continue to behave the same.  So I misspoke when 
I said things will "break" -- author expectations will break instead if 
they assume that that code which works on HTML elements would also work 
on SVG elements.

But maybe that's OK?