Hi,
[snip]
Two possible smartfont techniques for such locale feature are:
- alternate french punctuation marks with larger sidebearings: this is
very unflexible for users (punctuation characters without additional
space or with different space width are troublesome) but of course
simplifies the typesetting engines’ troubles the most.
- contextual variant of the <non breaking space> character: the
typesetter or their engine has to enter a space at the correct place
that then gets replaced by a (narrower) variant; here I think the
engine’s troubles aren’t really diminuished a lot, but the users’ might
rise. What’s more, contextual lookups that involve <space> don’t work
with XeTeX, so this is not very lucky here too.
As far as I know, TeX's view of spaces is to not handle them as
characters but as space without characters. So I don't understand, why
French Spacing should change in any way between pdftex and xetex. Space
without characters doesn't care for encoding nor fonts, because there is
no character to be encoded or handled in any way by a font.
Unicode already provides for a bunch of different space characters. IMO,
type designers should provide their fonts with appropriate space
characters (eg. 6-per-em space or thin space) and the typesetter or
their engine should check for the presence of that character and use it.
Even if whitespace is left to the font, which is perfectly reasonable
but not the TeX way, why should French Spacing be left to the font at all?
It's simply checking for a flag that says "I want French Spacing" and
then including white space (in whatever form) at appropriate places. You
can take appropriate white space from the font according to your liking
(there are many in space codepoints in unicode) or do it yourself. At
the most you can ask unicode to include a special "Space in front of
some punctuation in French"-codepoint, but I doubt that would be
successful nowadays.
BYe
Toscho
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