[css3-color] 'currentColor' change at parse time?

http://www.w3.org/TR/2003/CR-css3-color-20030514/#currentcolor says:
# If the 'currentColor' keyword is set on the 'color' property itself,
# it is treated as 'color:inherit' at parse time.

Why should this happen at parse time, rather than the time of value
computation?  It seems unusual, since I don't know of any other property
transformations that are specified as happening at parse time.

-David

-- 
L. David Baron                                <URL: http://dbaron.org/ >
           Technical Lead, Layout & CSS, Mozilla Corporation