[css-text] computed value for word-spacing:<percentage>

css-text-3 says that the computed value for word-spacing is “an absolute
length”, yet percentage values are defined to be relative to the advance
of the glyph for each word-separator character that word-spacing applies
to.  I think we need percentages not to compute down to an absolute
length, since you might have two different word-separator characters
whose advances are different within the one element.

-- 
Cameron McCormack ≝ http://mcc.id.au/