[css3-values] accessibility review

Hello CSS working group,

I've done a review of this spec for accessibility issues, but have not yet discussed it with PF.  This review does not constitute PF consensus.  I've copied the wai-xtech alias to allow PF to add any additional input.

http://www.w3.org/TR/css3-values/

5.1.1
Are 'ex' 'ch' 'rem' supported in any existing browsers?  These all seem fine for accessibility, but I'm curious why 'ex' and 'ch' are needed in addition to 'em'?  don't they do basically the same thing a using fractional 'em' units?

5.1.2
Are ' vw' 'vh' 'vmin' supported in any existing browsers?
Is there a way to specify a minimum absolute size for these?  It seems like this could easily get too small to read.
It does, however, seem useful for scalable/zooming UI

5.2
Please include a note that absolute units are sometimes problematic for accessibility, particularly when the output environment does not support zooming or resizing of absolute units

6.1 can you add an example of when one might use angle measurements in CSS?

6.3 frequency
Please add a note that frequencies near 7hz can cause seizures, and link to WCAG.  More detail in WCAG http://www.w3.org/WAI/WCAG20/quickref/20071211/Overview.php#seizure

8.3 attribute reference
It would be great to have an example of using this to style elements with ARIA attributes on them.  Would you be willing to work with PF and WCAG on a set of techniques around this, in addition to a simple example in the spec.