charsets.7: Update to reflect past developments

Rewrite the introduction to make Unicode's prominence more obvious.
Reformulate parts of the text to reflect current Unicode world.
Minor clarification for ASCII/ISO sections, some other minor fixes.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/charsets.7

@@ -11,62 +11,54 @@
 .\" This is combined from many sources, including notes by aeb and
 .\" research by esr.  Portions derive from a writeup by Roman Czyborra.
 .\"
-.\" Last changed by David Starner <dstarner98@aasaa.ofe.org>.
+.\" Changes also by David Starner <dstarner98@aasaa.ofe.org>.
 .\"
-.\" FIXME This page was written long ago, and various pieces are probably
+.TH CHARSETS 7 2014-06-05 "Linux" "Linux Programmer's Manual"
-.\" 	no longer quite current. A reworking by someone knowledgeable
-.\"	on charsets is needed. Among other things, the page needs to
-.\"	give more prominence to Unicode. mtk, May 2014
-.\"
-.TH CHARSETS 7 2014-05-28 "Linux" "Linux Programmer's Manual"
 .SH NAME
-charsets \- programmer's view of character sets and internationalization
+charsets - character set standards and internationalization
 .SH DESCRIPTION
-Linux is an international operating system.
+This manual page gives an overview on different character set standards
-Various of its utilities
+and how they were used on Linux before Unicode became ubiquitous.
-and device drivers (including the console driver) support multilingual
+Some of this information is still helpful for people working with legacy
-character sets including Latin-alphabet letters with diacritical
+systems and documents.
-marks, accents, ligatures, and entire non-Latin alphabets including
-Greek, Cyrillic, Arabic, and Hebrew.
 .LP
-This manual page presents a programmer's-eye view of different
+Standards discussed include such as
-character-set standards and how they fit together on Linux.
+ASCII, GB 2312, ISO 8859, JIS, KOI8-R, KS, and Unicode.
-Standards
+.LP
-discussed include ASCII, ISO 8859, KOI8-R, Unicode, ISO 2022 and
+The primary emphasis is on character sets that were actually used by
-ISO 4873.
+locale character sets, not the myriad others that could be found in data
-The primary emphasis is on character sets actually used as
-locale character sets, not the myriad others that can be found in data
 from other systems.
 .SS ASCII
 ASCII (American Standard Code For Information Interchange) is the original
 7-bit character set, originally designed for American English.
-It is currently described by the ECMA-6 standard.
+Also known as US-ASCII.
+It is currently described by the ISO 646:1991 IRV
+(International Reference Version) standard.
 .LP
 Various ASCII variants replacing the dollar sign with other currency
-symbols and replacing punctuation with non-English alphabetic characters
+symbols and replacing punctuation with non-English alphabetic
-to cover German, French, Spanish, and others in 7 bits exist.
+characters to cover German, French, Spanish, and others in 7 bits
-All are
+emerged.
-deprecated; glibc doesn't support locales whose character sets aren't
+All are deprecated;
-true supersets of ASCII.
+glibc does not support locales whose character sets are not true
-(These sets are also known as ISO-646, a close
+supersets of ASCII.
-relative of ASCII that permitted replacing these characters.)
 .LP
-As Linux was written for hardware designed in the US, it natively
+As Unicode, when using UTF-8, is ASCII-compatible, plain ASCII text
-supports ASCII.
+still renders properly on modern UTF-8 using systems.
 .SS ISO 8859
-ISO 8859 is a series of 15 8-bit character sets all of which have US
+ISO 8859 is a series of 15 8-bit character sets all of which have ASCII
-ASCII in their low (7-bit) half, invisible control characters in
+in their low (7-bit) half, invisible control characters in positions
-positions 128 to 159, and 96 fixed-width graphics in positions 160-255.
+128 to 159, and 96 fixed-width graphics in positions 160-255.
 .LP
-Of these, the most important is ISO 8859-1 (Latin-1).
+Of these, the most important is ISO 8859-1
-It is natively
+("Latin Alphabet No .1" / Latin-1).
-supported in the Linux console driver, fairly well supported in X11R6,
+It was widely adopted and supported by different systems,
-and is the base character set of HTML.
+and is gradually being replaced with Unicode.
+The ISO 8859-1 characters are also the first 256 characters of Unicode.
 .LP
 Console support for the other 8859 character sets is available under
 Linux through user-mode utilities (such as
 .BR setfont (8))
-.\" // some distributions still have the deprecated consolechars
 that modify keyboard bindings and the EGA graphics
 table and employ the "user mapping" font table in the console
 driver.
@@ -74,97 +66,85 @@ driver.
 Here are brief descriptions of each set:
 .TP
 8859-1 (Latin-1)
-Latin-1 covers most Western European languages such as Albanian, Catalan,
+Latin-1 covers many West European languages such as Albanian, Basque,
-Danish, Dutch, English, Faroese, Finnish, French, German, Galician,
+Danish, English, Faroese, Galician, German, Icelandic, Irish, Italian,
-Irish, Icelandic, Italian, Norwegian, Portuguese, Spanish, and
+Norwegian, Portuguese, Spanish, and Swedish.
-Swedish.
+The lack of the ligatures Dutch IJ/ij, French œ, and old-style „German“
-The lack of the ligatures Dutch ij, French oe and old-style
+quotation marks was considered tolerable.
-,,German`` quotation marks is considered tolerable.
 .TP
 8859-2 (Latin-2)
-Latin-2 supports most Latin-written Slavic and Central European
+Latin-2 supports many Latin-written Central and East European
-languages: Croatian, Czech, German, Hungarian, Polish, Romanian,
+languages such as Bosnian, Croatian, Czech, German, Hungarian, Polish,
 Slovak, and Slovene.
+Replacing Romanian ș/ț with ş/ţ was considered tolerable.
 .TP
 8859-3 (Latin-3)
-Latin-3 is popular with authors of Esperanto, Galician, and Maltese.
+Latin-3 was designed to cover of Esperanto, Maltese, and Turkish but
-(Turkish is now written with 8859-9 instead.)
+8859-9 later superseded it for Turkish.
 .TP
 8859-4 (Latin-4)
-Latin-4 introduced letters for Estonian, Latvian, and Lithuanian.
+Latin-4 introduced letters for North European languages such as
-It is essentially obsolete; see 8859-10 (Latin-6) and 8859-13 (Latin-7).
+Estonian, Latvian, Lithuanian but was superseded by 8859-10 and
+8859-13.
 .TP
 8859-5
 Cyrillic letters supporting Bulgarian, Byelorussian, Macedonian,
-Russian, Serbian, and Ukrainian.
+Russian, Serbian, and (almost completely) Ukrainian.
-Ukrainians read the letter "ghe"
+It was never widely used, see the discussion of KOI8-R/KOI8-U below.
-with downstroke as "heh" and would need a ghe with upstroke to write a
-correct ghe.
-See the discussion of KOI8-R below.
 .TP
 8859-6
-Supports Arabic.
+Was created for Arabic.
 The 8859-6 glyph table is a fixed font of separate
 letter forms, but a proper display engine should combine these
 using the proper initial, medial, and final forms.
 .TP
 8859-7
-Supports Modern Greek.
+Was created for modern Greek in 1987, updated in 2003.
 .TP
 8859-8
 Supports modern Hebrew without niqud (punctuation signs).
-Niqud and full-fledged Biblical Hebrew are outside the scope of this
+Niqud and full-fledged Biblical Hebrew were outside the scope of this
-character set; under Linux, UTF-8 is the preferred encoding for
+character set.
-these.
 .TP
 8859-9 (Latin-5)
 This is a variant of Latin-1 that replaces Icelandic letters with
 Turkish ones.
 .TP
 8859-10 (Latin-6)
-Latin 6 adds the last Inuit (Greenlandic) and Sami (Lappish) letters
+Latin-6 added Inuit (Greenlandic) and Sami (Lappish) letters that were 
-that were missing in Latin 4 to cover the entire Nordic area.
+missing in Latin-4 to cover the entire Nordic area.
-RFC 1345 listed a preliminary and different "latin6".
-Skolt Sami still
-needs a few more accents than these.
 .TP
 8859-11
-This exists only as a rejected draft standard.
+Supports the Thai alphabet and is nearly identical to the TIS-620
-The draft standard
+standard.
-was identical to TIS-620, which is used under Linux for Thai.
 .TP
 8859-12
 This set does not exist.
-While Vietnamese has been suggested for this
-space, it does not fit within the 96 (noncombining) characters ISO
-8859 offers.
-UTF-8 is the preferred character set for Vietnamese use
-under Linux.
 .TP
 8859-13 (Latin-7)
 Supports the Baltic Rim languages; in particular, it includes Latvian
 characters not found in Latin-4.
 .TP
 8859-14 (Latin-8)
-This is the Celtic character set, covering Gaelic and Welsh.
+This is the Celtic character set, covering Old Irish, Manx, Gaelic,
-This charset also contains the dotted characters needed for Old Irish.
+Welsh, Cornish, and Breton.
 .TP
 8859-15 (Latin-9)
-This adds the Euro sign and French and Finnish letters that were missing in
+Latin-9 is similar to widely used Latin-1 but replaces some less
-Latin-1.
+common symbols with the Euro sign and French and Finnish letters that
+were missing in Latin-1.
 .TP
 8859-16 (Latin-10)
-This set covers many of the languages covered by 8859-2, and supports
+This set covers many Southeast European languages, and most
-Romanian more completely than that set does.
+importantly supports Romanian more completely than Latin-2.
-.SS KOI8-R
+.SS KOI8-R / KOI8-U
-KOI8-R is a non-ISO character set popular in Russia.
+KOI8-R is a non-ISO character set popular in Russia before Unicode.
-The lower half
+The lower half is ASCII;
-is US ASCII; the upper is a Cyrillic character set somewhat better
+the upper is a Cyrillic character set somewhat better designed than
-designed than ISO 8859-5.
+ISO 8859-5.
-KOI8-U is a common character set, based off
+KOI8-U, based off KOI8-R, has better support for Ukrainian.
-KOI8-R, that has better support for Ukrainian.
+Neither of these sets are ISO-2022 compatible,
-Neither of these sets
+unlike the ISO-8859 series.
-are ISO-2022 compatible, unlike the ISO-8859 series.
 .LP
 Console support for KOI8-R is available under Linux through user-mode
 utilities that modify keyboard bindings and the EGA graphics table,
@@ -184,7 +164,7 @@ JIS X 0208 is used
 as a component to construct encodings such as EUC-JP, Shift_JIS,
 and ISO-2022-JP.
 EUC-JP is the most important encoding for Linux
-and includes US ASCII and JIS X 0208.
+and includes ASCII and JIS X 0208.
 In EUC-JP, JIS X 0208
 characters are expressed in two bytes, each of which is the
 JIS X 0208 code plus 0x80.
@@ -195,7 +175,7 @@ JIS X 0208, characters are mapped into a 94x94 two-byte matrix.
 KS X 1001 is used like JIS X 0208, as a component
 to construct encodings such as EUC-KR, Johab, and ISO-2022-KR.
 EUC-KR is the most important encoding for Linux and includes
-US ASCII and KS X 1001.
+ASCII and KS X 1001.
 KS C 5601 is an older name for KS X 1001.
 .SS GB 2312
 GB 2312 is a mainland Chinese national standard character set used
@@ -203,37 +183,31 @@ to express simplified Chinese.
 Just like JIS X 0208, characters are
 mapped into a 94x94 two-byte matrix used to construct EUC-CN.
 EUC-CN
-is the most important encoding for Linux and includes US ASCII and
+is the most important encoding for Linux and includes ASCII and
 GB 2312.
 Note that EUC-CN is often called as GB, GB 2312, or CN-GB.
 .SS Big5
-Big5 is a popular character set in Taiwan to express traditional
+Big5 was a popular character set in Taiwan to express traditional
 Chinese.
 (Big5 is both a character set and an encoding.)
-It is a superset of US ASCII.
+It is a superset of ASCII.
 Non-ASCII characters are expressed in two bytes.
 Bytes 0xa1-0xfe are used as leading bytes for two-byte characters.
-Big5 and its extension is widely used in Taiwan and Hong Kong.
+Big5 and its extension were widely used in Taiwan and Hong Kong.
-It is not ISO 2022-compliant.
+It is not ISO 2022 compliant.
-.SS TIS 620
+.SS TIS-620
-TIS 620 is a Thai national standard character set and a superset
+TIS-620 is a Thai national standard character set and a superset
-of US ASCII.
+of ASCII.
-Like ISO 8859 series, Thai characters are mapped into
+Like in the ISO 8859 series, Thai characters are mapped into
 0xa1-0xfe.
-TIS 620 is the only commonly used character set under
+.SS Unicode
-Linux besides UTF-8 to have combining characters.
+Unicode (ISO 10646) is a standard which aims to unambiguously represent
-.SS UNICODE
+every character in every human language.
-Unicode (ISO 10646) is a standard which aims to unambiguously represent every
-character in every human language.
 Unicode's structure permits 20.1 bits to encode every character.
-Since most computers don't include 20.1-bit
+Since most computers don't include 20.1-bit integers, Unicode is 
-integers, Unicode is usually encoded as 32-bit integers internally and
+usually encoded as 32-bit integers internally and either a series of 
-either a series of 16-bit integers (UTF-16) (needing two 16-bit integers
+16-bit integers (UTF-16) (needing two 16-bit integers only when 
-only when encoding certain rare characters) or a series of 8-bit bytes
+encoding certain rare characters) or a series of 8-bit bytes (UTF-8).
-(UTF-8).
-Information on Unicode is available at
-.UR http://www.unicode.org
-.UE .
 .LP
 Linux represents Unicode using the 8-bit Unicode Transformation Format
 (UTF-8).
@@ -258,19 +232,19 @@ into xxxxyyyy yyzzzzzz.
 (When UTF-8 is used to code the 31-bit ISO 10646
 then this progression continues up to 6-byte codes.)
 .LP
-For most people who use ISO-8859 character sets, this means that the
+For most texts in ISO-8859 character sets, this means that the
 characters outside of ASCII are now coded with two bytes.
 This tends
 to expand ordinary text files by only one or two percent.
 For Russian
-or Greek users, this expands ordinary text files by 100%, since text in
+or Greek texts, this expands ordinary text files by 100%, since text in
 those languages is mostly outside of ASCII.
 For Japanese users this means
 that the 16-bit codes now in common use will take three bytes.
-While there
+While there are algorithmic conversions from some character sets 
-are algorithmic conversions from some character sets (especially ISO-8859-1) to
+(especially ISO 8859-1) to Unicode, general conversion requires 
-Unicode, general conversion requires carrying around conversion tables,
+carrying around conversion tables, which can be quite large for 16-bit 
-which can be quite large for 16-bit codes.
+codes.
 .LP
 Note that UTF-8 is self-synchronizing: 10xxxxxx is a tail, any other
 byte is the head of a code.
@@ -288,22 +262,18 @@ Rendering of Unicode data streams is typically handled through
 "subfont" tables which map a subset of Unicode to glyphs.
 Internally
 the kernel uses Unicode to describe the subfont loaded in video RAM.
-This means that in UTF-8 mode one can use a character set with 512
+This means that the Linux console in UTF-8 mode one can use a character 
-different symbols.
+set with 512 different symbols.
 This is not enough for Japanese, Chinese and
 Korean, but it is enough for most other purposes.
 .LP
-At the current time, the console driver does not handle combining
-characters.
-So Thai, Sioux and any other script needing combining
-characters can't be handled on the console.
 .SS ISO 2022 and ISO 4873
 The ISO 2022 and 4873 standards describe a font-control model
 based on VT100 practice.
 This model is (partially) supported
 by the Linux kernel and by
 .BR xterm (1).
-It is popular in Japan and Korea.
+It used to be popular in Japan and Korea.
 .LP
 There are 4 graphic character sets, called G0, G1, G2, and G3,
 and one of them is the current character set for codes with
@@ -357,9 +327,8 @@ In particular, \fB^N\fP and \fB^O\fP are not used anymore, ESC ( xx
 can be used only with xx=B, and ESC ) xx, ESC * xx, ESC + xx
 are equivalent to ESC \- xx, ESC . xx, ESC / xx, respectively.
 .SH SEE ALSO
+.BR iconv (1),
 .BR console (4),
-.BR console_codes (4),
-.BR console_ioctl (4),
 .BR ascii (7),
 .BR iso_8859-1 (7),
 .BR unicode (7),