[bpt/emacs.git] / admin / notes / unicode

                                            -*-mode: text; coding: utf-8;-*-

Copyright (C) 2002-2013 Free Software Foundation, Inc.
See the end of the file for license conditions.

Problems, fixmes and other unicode-related issues
-------------------------------------------------------------

Notes by fx to record various things of variable importance.  handa
needs to check them -- don't take too seriously, especially with
regard to completeness.

 * SINGLE_BYTE_CHAR_P returns true for Latin-1 characters, which has
   undesirable effects.  E.g.:
   (multibyte-string-p (let ((s "x")) (aset s 0 ?£) s)) => nil
   (multibyte-string-p (concat [?£])) => nil
   (text-char-description ?£) => "M-#"

	These examples are all fixed by the change of 2002-10-14, but
	there still exist questionable SINGLE_BYTE_CHAR_P in the
	code (keymap.c and print.c).

 * Rationalize character syntax and its relationship to the Unicode
   database.  (Applies mainly to symbol an punctuation syntax.)

 * Fontset handling and customization needs work.  We want to relate
   fonts to scripts, probably based on the Unicode blocks.  The
   presence of small-repertoire 10646-encoded fonts in XFree 4 is a
   pain, not currently worked round.

	With the change on 2002-07-26, multiple fonts can be
	specified in a fontset for a specific range of characters.
	Each range can also be specified by script.  Before using
	ISO10646 fonts, Emacs checks their repertories to avoid such
	fonts that don't have a glyph for a specific character.

	fx has worked on fontset customization, but was stymied by
	basic problems with the way the default face is dealt with
	(and something else, I think).  This needs revisiting.

 * Work is also needed on charset and coding system priorities.

 * The relevant bits of latin1-disp.el need porting (and probably
   re-naming/updating).  See also cyril-util.el.

 * Quail files need more work now the encoding is largely irrelevant.

 * What to do with the old coding categories stuff?

 * The preferred-coding-system property of charsets should probably be
   junked unless it can be made more useful now.

 * find-multibyte-characters needs looking at.

 * Implement Korean cp949/UHC, BIG5-HKSCS and any other important missing
   charsets.

 * Lazy-load tables for unify-charset somehow?

	Actually, Emacs clears out all charset maps and unify-map just
	before dumping, and they are loaded again on demand by the
	dumped emacs.  But, those maps (char tables) generated while
	temacs is running can't be removed from the dumped emacs.

 * iso-2022 charsets get unified on i/o.

	With the change on 2003-01-06, decoding routines put `charset'
	property to decoded text, and iso-2022 encoder pay attention
	to it.  Thus, for instance, reading and writing by
	iso-2022-7bit preserve the original designation sequences.
	The property name `preferred-charset' may be better?

	We may have to utilize this property to decide a font.

 * Revisit locale processing: look at treating the language and
   charset parts separately.  (Language should affect things like
   spelling and calendar, but that's not a Unicode issue.)

 * Handle Unicode combining characters usefully, e.g. diacritics, and
   handle more scripts specifically (à la Devanagari).  There are
   issues with canonicalization.

 * We need tabular input methods, e.g. for maths symbols.  (Not
   specific to Unicode.)

 * Need multibyte text in menus, e.g. for the above.  (Not specific to
   Unicode -- see Emacs etc/TODO, but now mostly works with gtk.)

 * There's currently no support for Unicode normalization.

 * Populate char-width-table correctly for Unicode characters and
   worry about what happens when double-width charsets covering
   non-CJK characters are unified.

 * There are type errors lurking, e.g. in
   Fcheck_coding_systems_region.  Define ENABLE_CHECKING to find them.

 * Old auto-save files, and similar files, such as Gnus drafts,
   containing non-ASCII characters probably won't be re-read correctly.

\f
This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
Commit	Line	Data
c38e0c97	1	--mode: text; coding: utf-8;--
e88a2ed3	2
ab422c4d	3	Copyright (C) 2002-2013 Free Software Foundation, Inc.
e88a2ed3 GM	4	See the end of the file for license conditions.
	5
	6	Problems, fixmes and other unicode-related issues
	7	-------------------------------------------------------------
	8
	9	Notes by fx to record various things of variable importance. handa
	10	needs to check them -- don't take too seriously, especially with
	11	regard to completeness.
	12
	13	* SINGLE_BYTE_CHAR_P returns true for Latin-1 characters, which has
	14	undesirable effects. E.g.:
c38e0c97 PE	15	(multibyte-string-p (let ((s "x")) (aset s 0 ?£) s)) => nil
	16	(multibyte-string-p (concat [?£])) => nil
	17	(text-char-description ?£) => "M-#"
e88a2ed3 GM	18
	19	These examples are all fixed by the change of 2002-10-14, but
	20	there still exist questionable SINGLE_BYTE_CHAR_P in the
	21	code (keymap.c and print.c).
	22
	23	* Rationalize character syntax and its relationship to the Unicode
	24	database. (Applies mainly to symbol an punctuation syntax.)
	25
	26	* Fontset handling and customization needs work. We want to relate
	27	fonts to scripts, probably based on the Unicode blocks. The
	28	presence of small-repertoire 10646-encoded fonts in XFree 4 is a
	29	pain, not currently worked round.
	30
	31	With the change on 2002-07-26, multiple fonts can be
	32	specified in a fontset for a specific range of characters.
	33	Each range can also be specified by script. Before using
	34	ISO10646 fonts, Emacs checks their repertories to avoid such
	35	fonts that don't have a glyph for a specific character.
	36
	37	fx has worked on fontset customization, but was stymied by
	38	basic problems with the way the default face is dealt with
	39	(and something else, I think). This needs revisiting.
	40
	41	* Work is also needed on charset and coding system priorities.
	42
	43	* The relevant bits of latin1-disp.el need porting (and probably
	44	re-naming/updating). See also cyril-util.el.
	45
	46	* Quail files need more work now the encoding is largely irrelevant.
	47
	48	* What to do with the old coding categories stuff?
	49
	50	* The preferred-coding-system property of charsets should probably be
	51	junked unless it can be made more useful now.
	52
	53	* find-multibyte-characters needs looking at.
	54
	55	* Implement Korean cp949/UHC, BIG5-HKSCS and any other important missing
	56	charsets.
	57
	58	* Lazy-load tables for unify-charset somehow?
	59
	60	Actually, Emacs clears out all charset maps and unify-map just
	61	before dumping, and they are loaded again on demand by the
	62	dumped emacs. But, those maps (char tables) generated while
	63	temacs is running can't be removed from the dumped emacs.
	64
e88a2ed3 GM	65	* iso-2022 charsets get unified on i/o.
	66
	67	With the change on 2003-01-06, decoding routines put `charset'
	68	property to decoded text, and iso-2022 encoder pay attention
	69	to it. Thus, for instance, reading and writing by
	70	iso-2022-7bit preserve the original designation sequences.
	71	The property name `preferred-charset' may be better?
	72
	73	We may have to utilize this property to decide a font.
	74
	75	* Revisit locale processing: look at treating the language and
	76	charset parts separately. (Language should affect things like
	77	spelling and calendar, but that's not a Unicode issue.)
	78
	79	* Handle Unicode combining characters usefully, e.g. diacritics, and
c38e0c97	80	handle more scripts specifically (à la Devanagari). There are
e88a2ed3 GM	81	issues with canonicalization.
e88a2ed3 GM	82
e88a2ed3 GM	83	* We need tabular input methods, e.g. for maths symbols. (Not
	84	specific to Unicode.)
	85
	86	* Need multibyte text in menus, e.g. for the above. (Not specific to
	87	Unicode -- see Emacs etc/TODO, but now mostly works with gtk.)
	88
	89	* There's currently no support for Unicode normalization.
	90
	91	* Populate char-width-table correctly for Unicode characters and
	92	worry about what happens when double-width charsets covering
	93	non-CJK characters are unified.
	94
e88a2ed3 GM	95	* There are type errors lurking, e.g. in
	96	Fcheck_coding_systems_region. Define ENABLE_CHECKING to find them.
	97
e88a2ed3 GM	98	* Old auto-save files, and similar files, such as Gnus drafts,
	99	containing non-ASCII characters probably won't be re-read correctly.
	100
	101	\f
	102	This file is part of GNU Emacs.
	103
9ad5de0c	104	GNU Emacs is free software: you can redistribute it and/or modify
e88a2ed3	105	it under the terms of the GNU General Public License as published by
9ad5de0c GM	106	the Free Software Foundation, either version 3 of the License, or
9ad5de0c GM	107	(at your option) any later version.
e88a2ed3 GM	108
	109	GNU Emacs is distributed in the hope that it will be useful,
	110	but WITHOUT ANY WARRANTY; without even the implied warranty of
	111	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	112	GNU General Public License for more details.
	113
	114	You should have received a copy of the GNU General Public License
9ad5de0c	115	along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.