[css-text] Issue 18: character-based alignment in table columns

Issue 18 in CSS Text 4 asks:

>Is this intended to say that it’s the centers of the alignment characters
that should be aligned?
>It’s not clear that’s what it says, but that (or a different behavior)
needs to be specified,
>to describe what happens when different occurrences of the alignment
character
>are in different fonts. (Further, is that the intended behavior?
>Probably the most significant use case to consider is bold vs. non-bold
text,
>which only varies slightly in width.)

I've been looking at what InDesign does. It appears to align the origins of
the alignment character glyphs, which sometimes does not result in the
centers of the alignment characters being centered. I'm seeing similar
behavior from a TeX package I tried. This is consistent with the printed
examples we've found so far.

Dave