[css3-text] should 'tab-size' be in spaces or '0' characters?

http://dev.w3.org/csswg/css3-text/#tab-size defines a 'tab-size'
property taking an integer to be multiplied by the advance width of
the space (U+0020) character.

However, http://dev.w3.org/csswg/css3-values/#font-relative-lengths
defines the 'ch' unit as using the advance width of the '0' (U+0030)
character, which I believe was the result of implementation
experience that '0' produced good results for sizing in proportional
fonts, and made no difference in monospace fonts.  (I think that
implementation experience related specifically to sizing of text
inputs.)

Should 'tab-size' instead use the '0' width rather than the ' '
width?  I think I would prefer such a change.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂