RE: Merging combining classes, was: New contribution N2676

From: Jim Allan (
Date: Wed Oct 29 2003 - 08:39:53 CST

Kent Karlson posted:

> COMBINING COMMA BELOW is not "attached", even though cedilla is.
> A turned comma above is not _attached_ above...

Correct. COMBINING COMMA BELOW belongs to combining class 220.

However by Unicode specifications both it and an attached lower cedilla
on _g_ may be rendered by unattached turned comma above which interacts
with characters not in their respective combining classes. And this new
turned comma above of necessity would always be applied before normal
upper class 230 diacritics.

I don't see anything wrong with this in itself, but it is not what the
standard wording about combining classes suggests when taken on its own.

> Maybe an informative table is in order, giving which below diacritics
> may, or should, be rendered (turned) above, and for which base
> characters (latin/(greek/cyrillic?) small letters with descender?). I
> mean,
> there are other informative typographic tables in the standard, e.g.
> giving some Devanagari conjuncts.

Yes. That would be helpful.

One can not and should not expect font creators to know what
repositionings of diacritics from below to above are universally
acceptable and what repositionings are problematical.

I have no idea of the use of many diacritics in Unicode have and don't
necessarily know implemented alternate uses for diacritics which I do

It would be hazardous to guess whether changing the positions of such
diacritics would be acceptable to the users without guidance.

My feeling is that repositioning of an upper diacritic to a position
beneath a character should probably never be none (outside of funky,
display fonts which can make their own rules). Moving a lower diacritic
to a position above the base character is more likely to be acceptable.
But it should not in all such cases be turned.

For example turning U+031E COMBINING DOWN TACK BELOW if placing it above
a base character instead would turn it into its opposite in appearance,

Jim Allan

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