[CSS Transforms] syntax of transform-origin vs. background-position

Right now the syntax of the transform-origin property in
http://webkit.org/specs/CSSVisualEffects/CSSTransforms.html is
similar to the syntax of the existing 'background-position' property
(plus an extra length at the end for anybody implementing 3-D
transforms).  It actually looks like it pretty much matches the CSS
2.0 definition of background-position, but not the CSS 2.1
definition, which allows mixing of percentages/lengths with keywords
to match implementations.

I propose eliminating all differences with the background-position
property and just matching the CSS 2.1 definition of the
background-position property, plus (for those implementing 3-D
transforms) an optional third length at the end when the first two
values are percentages or lengths.

(There are also recently-agreed changes for css3-background; those
might make things a little trickier.)

-David

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