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bug#3526: 23.0.94; `list-character-sets' display

From: Kenichi Handa
Subject: bug#3526: 23.0.94; `list-character-sets' display
Date: Thu, 11 Jun 2009 09:52:29 +0900

In article <address@hidden>, "Drew Adams" <address@hidden> writes:

> What is a "supplementary character set"? Why are such sets listed
> separately? What sets are in the first, non "supplementary" list. IOW,
> why two lists, and what is the difference?

A supplementary character set is a character set defined
with `:supplementary-p' flag.  The meaning of this flag is
(in the docstring of define-charset):

VALUE must be nil or t.  If the VALUE is t, the charset is
supplementary, which means it is used only as a parent or a
subset of some other charset, or it is provided just for backward

For instance, gb18030-2-byte, gb18030-4-byte-bmp,
gb18030-4-byte-ext-1, gb18030-4-byte-ext-2, and
gb18030-4-byte-smp are all supplementary character sets to
define gb18030 which is a superset of the above all.

arabic-1-column, arabic-2-column, arabic-digit are also
supplementary character sets that are provided for backward

Priorities of supplementary character sets are always lower
than the other character set, so, for instance (char-charset
CHAR) never return a supplementary character set.

Kenichi Handa

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