Re: Canonical Combining Classes

From: Kenneth Whistler (
Date: Thu Jan 13 2000 - 17:45:44 EST

John Hudson asked:

> Thanks for this information, Ken. Am I right in thinking, though, that the
> classes I listed have not been bled off into combining class 0 in Unicode
> 3.0, since they are still listed in the current UnicodeData.txt file?


> I'm building some developer materials for type designers and font
> developers, and I want to be able to present as much of the Unicode
> character data as possible in immediately understandable terms. That is,
> I'm expanding the abbreviations and tags in the UnicodeData.txt files into
> simple definitions that will, in turn, be expanded into brief explanations.
> So it would be nice to have something other than this list of numbers for
> the 'fixed position class' entries in this field. Is there a list I can
> refer to somewhere?

No -- at least not other than the listing in Table 4-3 of the standard

Uwe's message earlier today provided some more information about the Tibetan
characters with fixed position combining classes.

A summary of the remaining fixed position classes:

10..26 Hebrew points
27..36 Arabic and Syriac vowelings
84 Telugu length mark (above)
91 Telugu length mark (below)
103 Thai vowels (below)
107 Thai tone marks (above)
118 Lao vowels (below)
122 Lao tone marks (above)
129 Tibetan a-chung (below)
130 Tibetan vowels (above)
132 Tibetan vowel (below)

The Hebrew and Arabic points were always fixed position classes, and
stayed that way. All of the Indic fixed position classes were bled
off to combining class 0, except those few occurring either above or
below the base character, where they had potential interactions with
other combining marks.

Note that combining class 0 contains many kinds of combining marks.
The significant point they share in common is that no other mark
will reorder around them when normalizing a decomposition.


> John Hudson
> Tiro Typeworks
> Vancouver, BC

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