RE: Merging combining classes, was: New contribution N2676

From: Peter Constable (
Date: Mon Oct 27 2003 - 12:46:33 CST

Philippe Verdy wrote:

> This principle may help solve the ambiguities in all those affected
> scripts
> (may be there are similar issues in the Latin script for Vietnamese,
> would like to better fit the phonetics of words that may be
> rendered by the currently requited normalization order of multiple
> Such issue also exists when there's a need to change the visual
> order of accents on Latin letters (for example if a macron should
> below or above a dieresis). In this case, the CCO control added to the
> general (Latin/Greek/Cyrillic) script would more likely be named

And Peter Kirk wrote:

> As
> you say, the same function may be needed in several scripts, including
> perhaps IPA which uses complex diacritic stacking.

There is no problem requiring a solution for combining marks used with
Latin script,* including IPA and Vietnamese, because all of the marks
that occupy a comparable space relative to the base have the same
combining class, meaning that normalization does not affect the order.
For such combinations, there is no "required normalization order".

So, for instance, the sequences < ..., combining macron, combining
diaeresis, ... > and < ..., combining diaeresis, combining macron, ... >
are both in canonical order and *not* canonically equivalent.

Peter Constable
Globalization Infrastructure and Font Technologies
Microsoft Windows Division

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