[whatwg] CSS2 system colors in legacy color values

[L. David Baron]

The "rules for parsing a legacy color value" in
http://www.whatwg.org/specs/web-apps/current-work/complete/common-microsyntaxes.html#rules-for-parsing-a-legacy-color-value
specify that CSS2 system colors should be accepted, and that they
should be converted to a simple color.

It seems like a substantial amount of work to get dynamic change
handling correct for this case, since system colors can change
dynamically when the user changes system appearance.  I'd really
like to avoid having to add dynamic change handling for this, and
I'd also like to avoid having to make system colors dynamic in CSS
but static in HTML.

What was the motivation for adding support for CSS2 system colors
(which I would note are deprecated in css3-color) to legacy HTML
color values?  What implementations support them, and do they
respond to dynamic changes properly?

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/