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diff --git a/man7/unicode.7 b/man7/unicode.7 new file mode 100644 index 0000000..f65a9b2 --- /dev/null +++ b/man7/unicode.7 @@ -0,0 +1,246 @@ +.\" Copyright (C) Markus Kuhn, 1995, 2001 +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" 1995-11-26 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de> +.\" First version written +.\" 2001-05-11 Markus Kuhn <mgk25@cl.cam.ac.uk> +.\" Update +.\" +.TH unicode 7 2023-03-12 "Linux man-pages 6.05.01" +.SH NAME +unicode \- universal character set +.SH DESCRIPTION +The international standard ISO/IEC 10646 defines the +Universal Character Set (UCS). +UCS contains all characters of all other character set standards. +It also guarantees "round-trip compatibility"; +in other words, +conversion tables can be built such that no information is lost +when a string is converted from any other encoding to UCS and back. +.PP +UCS contains the characters required to represent practically all +known languages. +This includes not only the Latin, Greek, Cyrillic, +Hebrew, Arabic, Armenian, and Georgian scripts, but also Chinese, +Japanese and Korean Han ideographs as well as scripts such as +Hiragana, Katakana, Hangul, Devanagari, Bengali, Gurmukhi, Gujarati, +Oriya, Tamil, Telugu, Kannada, Malayalam, Thai, Lao, Khmer, Bopomofo, +Tibetan, Runic, Ethiopic, Canadian Syllabics, Cherokee, Mongolian, +Ogham, Myanmar, Sinhala, Thaana, Yi, and others. +For scripts not yet +covered, research on how to best encode them for computer usage is +still going on and they will be added eventually. +This might +eventually include not only Hieroglyphs and various historic +Indo-European languages, but even some selected artistic scripts such +as Tengwar, Cirth, and Klingon. +UCS also covers a large number of +graphical, typographical, mathematical, and scientific symbols, +including those provided by TeX, Postscript, APL, MS-DOS, MS-Windows, +Macintosh, OCR fonts, as well as many word processing and publishing +systems, and more are being added. +.PP +The UCS standard (ISO/IEC 10646) describes a +31-bit character set architecture +consisting of 128 24-bit +.IR groups , +each divided into 256 16-bit +.I planes +made up of 256 8-bit +.I rows +with 256 +.I column +positions, one for each character. +Part 1 of the standard (ISO/IEC 10646-1) +defines the first 65534 code positions (0x0000 to 0xfffd), which form +the +.I Basic Multilingual Plane +(BMP), that is plane 0 in group 0. +Part 2 of the standard (ISO/IEC 10646-2) +adds characters to group 0 outside the BMP in several +.I "supplementary planes" +in the range 0x10000 to 0x10ffff. +There are no plans to add characters +beyond 0x10ffff to the standard, therefore of the entire code space, +only a small fraction of group 0 will ever be actually used in the +foreseeable future. +The BMP contains all characters found in the +commonly used other character sets. +The supplemental planes added by +ISO/IEC 10646-2 cover only more exotic characters for special scientific, +dictionary printing, publishing industry, higher-level protocol and +enthusiast needs. +.PP +The representation of each UCS character as a 2-byte word is referred +to as the UCS-2 form (only for BMP characters), +whereas UCS-4 is the representation of each character by a 4-byte word. +In addition, there exist two encoding forms UTF-8 +for backward compatibility with ASCII processing software and UTF-16 +for the backward-compatible handling of non-BMP characters up to +0x10ffff by UCS-2 software. +.PP +The UCS characters 0x0000 to 0x007f are identical to those of the +classic US-ASCII +character set and the characters in the range 0x0000 to 0x00ff +are identical to those in +ISO 8859-1 (Latin-1). +.SS Combining characters +Some code points in UCS +have been assigned to +.IR "combining characters" . +These are similar to the nonspacing accent keys on a typewriter. +A combining character just adds an accent to the previous character. +The most important accented characters have codes of their own in UCS, +however, the combining character mechanism allows us to add accents +and other diacritical marks to any character. +The combining characters +always follow the character which they modify. +For example, the German +character Umlaut-A ("Latin capital letter A with diaeresis") can +either be represented by the precomposed UCS code 0x00c4, or +alternatively as the combination of a normal "Latin capital letter A" +followed by a "combining diaeresis": 0x0041 0x0308. +.PP +Combining characters are essential for instance for encoding the Thai +script or for mathematical typesetting and users of the International +Phonetic Alphabet. +.SS Implementation levels +As not all systems are expected to support advanced mechanisms like +combining characters, ISO/IEC 10646-1 specifies the following three +.I implementation levels +of UCS: +.TP 0.9i +Level 1 +Combining characters and Hangul Jamo +(a variant encoding of the Korean script, where a Hangul syllable +glyph is coded as a triplet or pair of vowel/consonant codes) are not +supported. +.TP +Level 2 +In addition to level 1, combining characters are now allowed for some +languages where they are essential (e.g., Thai, Lao, Hebrew, +Arabic, Devanagari, Malayalam). +.TP +Level 3 +All UCS characters are supported. +.PP +The Unicode 3.0 Standard +published by the Unicode Consortium +contains exactly the UCS Basic Multilingual Plane +at implementation level 3, as described in ISO/IEC 10646-1:2000. +Unicode 3.1 added the supplemental planes of ISO/IEC 10646-2. +The Unicode standard and +technical reports published by the Unicode Consortium provide much +additional information on the semantics and recommended usages of +various characters. +They provide guidelines and algorithms for +editing, sorting, comparing, normalizing, converting, and displaying +Unicode strings. +.SS Unicode under Linux +Under GNU/Linux, the C type +.I wchar_t +is a signed 32-bit integer type. +Its values are always interpreted +by the C library as UCS +code values (in all locales), a convention that is signaled by the GNU +C library to applications by defining the constant +.B __STDC_ISO_10646__ +as specified in the ISO C99 standard. +.PP +UCS/Unicode can be used just like ASCII in input/output streams, +terminal communication, plaintext files, filenames, and environment +variables in the ASCII compatible UTF-8 multibyte encoding. +To signal the use of UTF-8 as the character +encoding to all applications, a suitable +.I locale +has to be selected via environment variables (e.g., +"LANG=en_GB.UTF-8"). +.PP +The +.B nl_langinfo(CODESET) +function returns the name of the selected encoding. +Library functions such as +.BR wctomb (3) +and +.BR mbsrtowcs (3) +can be used to transform the internal +.I wchar_t +characters and strings into the system character encoding and back +and +.BR wcwidth (3) +tells how many positions (0\[en]2) the cursor is advanced by the +output of a character. +.SS Private Use Areas (PUA) +In the Basic Multilingual Plane, +the range 0xe000 to 0xf8ff will never be assigned to any characters by +the standard and is reserved for private usage. +For the Linux +community, this private area has been subdivided further into the +range 0xe000 to 0xefff which can be used individually by any end-user +and the Linux zone in the range 0xf000 to 0xf8ff where extensions are +coordinated among all Linux users. +The registry of the characters +assigned to the Linux zone is maintained by LANANA and the registry +itself is +.I Documentation/admin\-guide/unicode.rst +in the Linux kernel sources +.\" commit 9d85025b0418163fae079c9ba8f8445212de8568 +(or +.I Documentation/unicode.txt +before Linux 4.10). +.PP +Two other planes are reserved for private usage, plane 15 +(Supplementary Private Use Area-A, range 0xf0000 to 0xffffd) +and plane 16 (Supplementary Private Use Area-B, range +0x100000 to 0x10fffd). +.SS Literature +.IP \[bu] 3 +Information technology \[em] Universal Multiple-Octet Coded Character +Set (UCS) \[em] Part 1: Architecture and Basic Multilingual Plane. +International Standard ISO/IEC 10646-1, International Organization +for Standardization, Geneva, 2000. +.IP +This is the official specification of UCS. +Available from +.UR http://www.iso.ch/ +.UE . +.IP \[bu] +The Unicode Standard, Version 3.0. +The Unicode Consortium, Addison-Wesley, +Reading, MA, 2000, ISBN 0-201-61633-5. +.IP \[bu] +S.\& Harbison, G.\& Steele. C: A Reference Manual. Fourth edition, +Prentice Hall, Englewood Cliffs, 1995, ISBN 0-13-326224-3. +.IP +A good reference book about the C programming language. +The fourth +edition covers the 1994 Amendment 1 to the ISO C90 standard, which +adds a large number of new C library functions for handling wide and +multibyte character encodings, but it does not yet cover ISO C99, +which improved wide and multibyte character support even further. +.IP \[bu] +Unicode Technical Reports. +.RS +.UR http://www.unicode.org\:/reports/ +.UE +.RE +.IP \[bu] +Markus Kuhn: UTF-8 and Unicode FAQ for UNIX/Linux. +.RS +.UR http://www.cl.cam.ac.uk\:/\[ti]mgk25\:/unicode.html +.UE +.RE +.IP \[bu] +Bruno Haible: Unicode HOWTO. +.RS +.UR http://www.tldp.org\:/HOWTO\:/Unicode\-HOWTO.html +.UE +.RE +.\" .SH AUTHOR +.\" Markus Kuhn <mgk25@cl.cam.ac.uk> +.SH SEE ALSO +.BR locale (1), +.BR setlocale (3), +.BR charsets (7), +.BR utf\-8 (7) |