CPAN.pm sync

[p5sagit/p5-mst-13.2.git] / ext / Encode / lib / Encode / Supported.pod

=head1 NAME

Encode::Supported -- Supported encodings by Encode

=head1 DESCRIPTION

=head2 Encoding Names

Encoding names are case insensitive. White space in names
is ignored.  In addition an encoding may have aliases.
Each encoding has one "canonical" name.  The "canonical"
name is chosen from the names of the encoding by picking
the first in the following sequence (with a few exceptions).

=over

=item *

The name used by the Perl community.  That includes 'utf8' and 'ascii'.
Unlike aliases, canonical names directly reach the method so such
frequently used words like 'utf8' don't need to do alias lookups.

=item *

The MIME name as defined in IETF RFCs  This includes all "iso-"'s.

=item * 

The name in the IANA registry.

=item *

The name used by the organization that defined it.

=back

In case I<de jure> canonical names differ from that of the Encode
module, they are always aliased if it ever be implemented.  So you can
safely tell if a given encoding is implemented or not just by passing 
the canonical name.

Because of all the alias issues, and because in the general case 
encodings have state, "Encode" uses an encoding object internally 
once an operation is in progress.

=head1 Supported Encodings

As of Perl 5.8.0, at least the following encodings are recognized.
Note that unless otherwise specified, they are all case insensitive
(via alias) and all occurrence of spaces are replaced with '-'.
In other words, "ISO 8859 1" and "iso-8859-1" are identical.

Encodings are categorized and implemented in several different modules
but you don't have to C<use Encode::XX> to make them available for
most cases.  Encode.pm will automatically load those modules on demand.

=head2 Built-in Encodings

The following encodings are always available.

  Canonical     Aliases                      Comments & References
  ----------------------------------------------------------------
  ascii         US-ascii                                    [ECMA]
  iso-8859-1    latin1                                       [ISO]
  utf8          UTF-8                                    [RFC2279]
  ----------------------------------------------------------------

=head2 Encode::Unicode -- other Unicode encodings

Unicode coding schemes other than native utf8 are supported by
Encode::Unicode which will be autoloaded on demand.

  ----------------------------------------------------------------
  UCS-2BE       UCS-2, iso-10646-1                      [IANA, UC]
  UCS-2LE                                                     [UC]
  UTF-16                                                      [UC]
  UTF-16BE                                                    [UC]
  UTF-16LE                                                    [UC]
  UTF-32                                                      [UC]
  UTF-32BE                                                    [UC]
  UTF-32LE                                                    [UC]
  ----------------------------------------------------------------

To find how those (UCS-2|UTF-(16|32))(LE|BE)? differ to one another,
see L<Encode::Unicode>. 

=head2 Encode::Byte -- Extended ASCII

Encode::Byte implements most of single-byte encodings except for
Symbols and EBCDIC. The following encodings are based single-byte
encoding implemented as extended ASCII.  For most cases it uses
\x80-\xff (upper half) to map non-ASCII characters.

=over 2

=item ISO-8859 and corresponding vendor mappings

Since there are so many, they are presented in table format with
languages and corresponding encoding names by vendors.  Note the table
is sorted in order of ISO-8859 and the corresponding vendor mappings
are slightly different from that of ISO.  See
L<http://czyborra.com/charsets/iso8859.html> for details.

  Lang/Regions  ISO/Other Std.  DOS     Windows Macintosh  Others
  ----------------------------------------------------------------
  N. America    (ASCII)         cp437        AdobeStandardEncoding
                                cp863 (DOSCanadaF)
  W.  Europe    iso-8859-1     cp850   cp1252  MacRoman  nextstep
                                                         hp-roman8
                                cp860 (DOSPortuguese)
  Cntrl. Europe iso-8859-2      cp852   cp1250  MacCentralEurRoman
                                                MacCroatian
                                                MacRomanian
                                                MacRumanian
  Latin3 [1]    iso-8859-3      
  Latin4 [2]    iso-8859-4              
  Cyrillics     iso-8859-5      cp855   cp1251  MacCyrillic
    (Also see next section)     cp866           MacUkrainian
  Arabic        iso-8859-6      cp864   cp1256  MacArabic
                                cp1006          MacFarsi
  Greek         iso-8859-7      cp737   cp1253  MacGreek
                                cp869 (DOSGreek2)
  Hebrew        iso-8859-8      cp862   cp1255  MacHebrew
  Turkish       iso-8859-9      cp857   cp1254  MacTurkish
  Nordics       iso-8859-10     cp865
                                cp861           MacIcelandic
                                                MacSami
  Thai          iso-8859-11 [3] cp874           MacThai
  (iso-8859-12 is nonexistent. Reserved for Indics?)
  Baltics       iso-8859-13     cp775           cp1257
  Celtics       iso-8859-14
  Latin9 [4]    iso-8859-15
  Latin10       iso-8859-16
  Vietnamese    viscii                  cp1258  MacVietnamese
  ----------------------------------------------------------------

  [1] Esperanto, Maltese, and Turkish. Turkish is now on 8859-5.
  [2] Baltics.  Now on 8859-10.
  [3] Also know as TIS 620. 
  [4] Nicknamed Latin0; Euro sign as well as French and Finnish
      letters that are missing from 8859-1 are added.

All cp* are also available as ibm-*, ms-*, and windows-* .  See also
L<http://czyborra.com/charsets/codepages.html>.

Macintosh encodings don't seem to be registered in such entities as
IANA.  "Canonical" names in Encode are based upon Apple's Tech Note
1150.  See L<http://developer.apple.com/technotes/tn/tn1150.html> 
for details

=item KOI8 - De Facto Standard for Cyrillic world

Though ISO-8859 does have ISO-8859, KOI8 series is far more popular
in the Net.   L<Encode> comes with the following KOI charsets.
For gory details, see L<http://czyborra.com/charsets/cyrillic.html>

  ----------------------------------------------------------------
  koi8-f                                        
  koi8-r cp878                                           [RFC1489]
  koi8-u                                                 [RFC2319]

=item gsm0338 - Hentai Latin 1

GSM0338 is for GSM handsets. Though it shares alphanumerals with
ASCII, control character ranges and other parts are mapped very
differently, presumably to store Greek and Cyrillic alphabets.
This is also covered in Encode::Byte even though it does not
comply to extended ASCII.

=back

=head2 The CJK: Chinese, Japanese, Korean (Multibyte)

Note that Vietnamese is listed above.  Also read "Encoding vs Charset"
below.  Also note these are implemented in distinct module by
languages, due the the size concerns.  Please refer to their
respective document pages.

=over 4

=item Encode::CN -- Continental China

  Standard      DOS/Win Macintosh                Comment/Reference
  ----------------------------------------------------------------
  euc-cn [1]            MacChineseSimp
  (gbk)         cp936 [2]
  gb12345-raw                      { GB12345 without CES }
  gb2312-raw                       { GB2312  without CES }
  hz
  iso-ir-165
  ----------------------------------------------------------------

  [1] GB2312 is aliased to this.  see L<Microsoft-related naming mess>
  [2] gbk is aliased to this. see L<Microsoft-related naming mess>

=item Encode::JP -- Japan

  Standard      DOS/Win Macintosh                Comment/Reference
  ----------------------------------------------------------------
  euc-jp
  shiftjis      cp932   macJapanese
  7bit-jis
  euc-jp
  iso-2022-jp                                            [RFC1468]
  iso-2022-jp-1                                          [RFC2237]
  jis0201-raw  { JIS X 0201 (roman + halfwidth kana) without CES }
  jis0208-raw  { JIS X 0208 (Kanji + fullwidth kana) without CES }
  jis0212-raw  { JIS X 0212 (Extended Kanji)         without CES }
  ----------------------------------------------------------------

=item Encode::KR -- Korea

  Standard      DOS/Win Macintosh                Comment/Reference
  ----------------------------------------------------------------
  euc-kr                MacKorean                        [RFC1557]
                cp949 [1]                    
  iso-2022-kr                                            [RFC1557]
  johab                                  [KS X 1001:1998, Annex 3]
  ksc5601-raw                              { KSC5601 without CES }
  ----------------------------------------------------------------

  [1] ks_c_5601-1987, (x-)?windows-949, and uhc are aliased to this.
  See below.

=item Encode::TW -- Taiwan

  Standard      DOS/Win Macintosh                Comment/Reference
  ----------------------------------------------------------------
  big5          cp950   MacChineseTrad
  big5-hkscs
  ----------------------------------------------------------------

=item Encode::HanExtra -- More Chinese via CPAN

Due to size concerns, additional Chinese encodings below are
distributed separately on CPAN, under the name Encode::HanExtra.

  Standard      DOS/Win Macintosh                Comment/Reference
  ----------------------------------------------------------------
  gb18030
  euc-tw
  big5plus
  ----------------------------------------------------------------

=back

=head2 Miscellaneous encodings

=over 4

=item Encode::EBCDIC

See L<perlebcdic> for details.

  ----------------------------------------------------------------
  cp37
  cp500  
  cp875  
  cp1026  
  cp1047  
  posix-bc
  ----------------------------------------------------------------

=item Encode::Symbols

For symbols  and dingbats.

  ----------------------------------------------------------------
  symbol
  dingbats
  MacDingbats
  AdobeZdingbat
  AdobeSymbol
  ----------------------------------------------------------------

=back

=head1 Unsupported encodings

The following are not supported as yet.  Some because they are rarely
used, some because of technical difficulties.  They may be supported by
external modules via CPAN in future, however.

=over 4

=item   ISO-2022-JP-2 [RFC1554]

Not very popular yet.  Needs Unicode Database or equivalent to
implement encode() (Because it includes JIS X 0208/0212, KSC5601, and
GB2312 simultaneously, which code points in Unicode overlap.  So you
need to lookup the database to determine what character set a given
Unicode character should belong). 

=item ISO-2022-CN [RFC1922]

Not very popular.  Needs CNS 11643-1 and 2 which are not available in
this module.  CNS 11643 is supported (via euc-tw) in Encode::HanExtra.
Autrijus may add support for this encoding in his module in future.

=item various UP-UX encodings

The following are unsupported due to the lack of mapping data.

  '8'  - arabic8, greek8, hebrew8, kana8, thai8, and turkish8
  '15' - japanese15, korean15, and roi15

=item Cyrillic encoding ISO-IR-111

Anton doubts its usefulness.

=item ISO-8859-8-1 [Hebrew]

None of the Encode team knows Hebrew enough (ISO-8859-8, cp1255 and
MacHebrew are supported because and just because there were mappings
available at L<http://www.unicode.org/>).  Contributions welcome.

=item ISIRI 3342, Iran System, ISIRI 2900 [Farsi]

Ditto.

=item Thai encoding TCVN

Ditto.

=item Vietnamese encodings VPS

Though Jungshik has reported that Mozilla supports this encoding it
was too late before 5.8.0 for us to add one.  In future via a separate
module.  See
L<http://lxr.mozilla.org/seamonkey/source/intl/uconv/ucvlatin/vps.uf>
and
L<http://lxr.mozilla.org/seamonkey/source/intl/uconv/ucvlatin/vps.ut>
if you are interested in helping us.

=item Various Mac encodings

The following are unsupported due to the lack of mapping data. 

  MacArmenian,  MacBengali,   MacBurmese,   MacEthiopic
  MacExtArabic, MacGeorgian,  MacKannada,   MacKhmer
  MacLaotian,   MacMalayalam, MacMongolian, MacOriya
  MacSinhalese, MacTamil,     MacTelugu,    MacTibetan
  MacVietnamese

The rest of which already available are based upon the vendor mappings
at L<http://www.unicode.org/Public/MAPPINGS/VENDORS/APPLE/> .

=item (Mac) Indic encodings

The maps for the following is available at L<http://www.unicode.org/>
but remains unsupport because those encodings need algorithmical
approach, currently unsupported by F<enc2xs>

  MacDevanagari
  MacGurmukhi
  MacGujarati

For details, please see C<Unicode mapping issues and notes:> at
L<http://www.unicode.org/Public/MAPPINGS/VENDORS/APPLE/DEVANAGA.TXT> .

I believe this issue is prevalent not only for Mac Indics but also in
other Indic encodings, but the above were the only Indic encodings
maps that I could find at L<http://www.unicode.org/> .

=back

=head1 Encoding vs. Charset -- terminology

We are used to using the term (character) I<encoding> and I<character set>
interchangeably.  But just as using the term byte and character is
dangerous and should be differentiated when needed, we need to
differentiate I<encoding> and I<character set>.

To understand that, it's follow how we make computers grok our characters.

=over 4

=item *

First we start with which characters to include.  We call this
collection of characters I<character repertoire>.

=item *

Then we have to give each character a unique ID so your computer can
tell the difference from 'a' to 'A'.  This itemized character
repertoire is now a I<character set>.

=item *

If your computer can grow the character set without further
processing, you can go ahead use it.  This is called a I<coded
character set> (CCS) or I<raw character encoding>.  ASCII is used this
way for most cases.

=item *

But in many cases especially multi-byte CJK encodings, you have to
tweak a little more.  Your network connection may not accept any data
with the Most Significant Bit set, Your computer may not be able to
tell if a given byte is a whole character or just half of it.  So you
have to I<encode> the character set to use it.

A I<character encoding scheme> (CES) determines how to encode a given
character set, or a set of multiple character sets.  7bit ISO-2022 is
an example of CES.  You switch between character sets via I<escape
sequence>.

=back

Technically, or Mathematically speaking, a character set encoded in
such a CES that maps character by character may form a CCS.  EUC is such
an example.  CES of EUC is as follows;

=over 4

=item *

Map ASCII unchanged.

=item *

Map such a character set that consists of 94 or 96 powered by N
members by adding 0x80 to each byte.

=item *

You can also use 0x8e and 0x8f to tell the following sequence of
characters belong to yet another character set.  each following byte
is added by 0x80

=back

By carefully looking at at the encoded byte sequence, you may find the
byte sequence conforms a unique number.  In that sense EUC is a CCS
generated by a CES above from up to four CCS (complicated?).  UTF-8
falls into this category.  See L<perlUnicode/"UTF-8"> to find how
UTF-8 maps Unicode to a byte sequence.

You may also find by now why 7bit ISO-2022 cannot conform a CCS.  If
you look at a byte sequence \x21\x21, you can't tell if it is two !'s
or IDEOGRAPHIC SPACE.  EUC maps the latter to \xA1\xA1 so you have no
trouble between "!!". and "  "  

=head1 Encoding Classification (by Anton Tagunov and Dan Kogai)

This section tries to classify the supported encodings by their 
applicability for information exchange over the Internet and to 
choose the most suitable aliases to name them in the context of 
such communication.

=over 2

=item * 

To (en|de) code Encodings marked as C<(**)>, You need 
C<Encode::HanExtra>, available from CPAN.

=back

Encoding names

  US-ASCII    UTF-8    ISO-8859-*  KOI8-R
  Shift_JIS   EUC-JP   ISO-2022-JP ISO-2022-JP-1
  EUC-KR      Big5     GB2312

are registered to IANA as preferred MIME names and may probably 
be used over the Internet.

C<Shift_JIS> has been officialized by JIS X 0208:1997.
L<Microsoft-related naming mess> gives details.

C<GB2312> is the IANA name for C<EUC-CN>.
See L<Microsoft-related naming mess> for details.

C<GB_2312-80> I<raw> encoding is available as C<gb2312-raw>
with Encode. See L<Encode::CN> for details.

  EUC-CN
  KOI8-U        [RFC2319]

have not been registered with IANA (as of March 2002) but
seem to be supported by major web browsers. 
IANA name for C<EUC-CN> is C<GB2312>.

  KS_C_5601-1987

is heavily misused.
See L<Microsoft-related naming mess> for details.

C<KS_C_5601-1987> I<raw> encoding is available as C<kcs5601-raw>
with Encode. See L<Encode::KR> for details.

  UTF-16 UTF-16BE UTF-16LE

are IANA-registered C<charset>s. See [RFC 2781] for details.
Jungshik Shin reports that UTF-16 with a BOM is well accepted
by MS IE 5/6 and NS 4/6. Beware however that

=over 2

=item *

C<UTF-16> support in any software you're going to be
using/interoperating with has probably been less tested
then C<UTF-8> support

=item *

C<UTF-8> coded data seamlessly passes traditional
command piping (C<cat>, C<more>, etc.) while C<UTF-16> coded
data is likely to cause confusion (with it's zero bytes,
for example)

=item *

it is beyond the power of words to describe the way HTML browsers
encode non-C<ASCII> form data. To get a general impression visit
L<http://ppewww.ph.gla.ac.uk/~flavell/charset/form-i18n.html>.
While encoding of form data has stabilized for C<UTF-8> coded pages
(at least IE 5/6, NS 6, Opera 6 behave consistently), be sure to
expect fun (and cross-browser discrepancies) with C<UTF-16> coded
pages!

=back

The rule of thumb is to use C<UTF-8> unless you know what
you're doing and unless you really benefit from using C<UTF-16>.


  ISO-IR-165    [RFC1345]
  VISCII
  GB 12345
  GB 18030 (**)  (see links bellow)
  EUC-TW   (**)

are totally valid encodings but not registered at IANA.
The names under which they are listed here are probably the
most widely-known names for these encodings and are recommended
names.

  BIG5PLUS (**)

is a bit proprietary name. 

=head2 Microsoft-related naming mess

Microsoft products misuse the following names:

=over 2

=item KS_C_5601-1987

Microsoft extension to C<EUC-KR>.

Proper names: C<CP949>, C<UHC>, C<x-windows-949> (as used by Mozilla).

See L<http://lists.w3.org/Archives/Public/ietf-charsets/2001AprJun/0033.html>
for details.

Encode aliases C<KS_C_5601-1987> to C<cp949> to reflect this common
misusage. I<Raw> C<KS_C_5601-1987> encoding is available as
C<kcs5601-raw>.

See L<Encode::KR> for details.

=item GB2312

Microsoft extension to C<EUC-CN>.

Proper names: C<CP936>, C<GBK>.

C<GB2312> has been registered in the C<EUC-CN> meaning at
IANA. This has partially repaired the situation: Microsoft's 
C<GB2312> has become a superset of the official C<GB2312>.

Encode aliases C<GB2312> to C<euc-cn> in full agreement with
IANA registration. C<cp936> is supported separately.
I<Raw> C<GB_2312-80> encoding is available as C<gb2312-raw>.

See L<Encode::CN> for details.

=item Big5

Microsoft extension to C<Big5>.

Proper name: C<CP950>.

Encode separately supports C<Big5> and C<cp950>.

=item Shift_JIS

Microsoft's understanding of C<Shift_JIS>.

JIS has not endorsed the full Microsoft standard however.
The official C<Shift_JIS> includes only JIS X 0201 and JIS X 0208
subsets, while Microsoft has always been meaning C<Shift_JIS> to
encode a wider character repertoire. See C<IANA> registration for
C<Windows-31J>.

As a historical predecessor Microsoft's variant
probably has more rights for the name, albeit it may be objected
that Microsoft shouldn't have used JIS as part of the name
in the first place.

Unambiguous name: C<CP932>. C<IANA> name (not used?): C<Windows-31J>.

Encode separately supports C<Shift_JIS> and C<cp932>.

=back

=head1 Glossary

=over 2

=item character repertoire

A collection of unique characters.  A I<character> set in the most
strict sense. At this stage characters are not numbered.

=item coded character set (CCS)

A character set that is mapped in a way computers can use directly.
Many character encodings including EUC falls in this category.

=item character encoding scheme (CES)

An algorithm to map a character set to a byte sequence.  You don't
have to be able to tell which character set a given byte sequence
belongs.  7-bit ISO-2022 is a CES but it cannot be a CCS.  EUC is an
example of being both a CCS and CES.

=item charset (in MIME context)

has long been used in the meaning of C<encoding>, CES.

While C<character set> word combination has lost this meaning
in MIME context since [RFC 2130], C<charset> abbreviation has
retained it. This is how [RFC 2277], [RFC 2278] bless C<charset>:


 This document uses the term "charset" to mean a set of rules for
 mapping from a sequence of octets to a sequence of characters, such
 as the combination of a coded character set and a character encoding
 scheme; this is also what is used as an identifier in MIME "charset="
 parameters, and registered in the IANA charset registry ...  (Note
 that this is NOT a term used by other standards bodies, such as ISO).
                                               [RFC 2277]

=item EUC

Extended Unix Character.  See ISO-2022

=item ISO-2022

A CES that was carefully designed to coexist with ASCII.  There are 7
bit version and 8 bit version.  

7 bit version switches character set via escape sequence so this
cannot form a CCS.  Since this is more difficult to handle in programs
than the 8 bit version, 7 bit version is not very popular except for
iso-2022-jp, the de facto standard CES for e-mails.

8 bit version can conform a CCS.  EUC and ISO-8859 are two examples
thereof.  Pre-5.6 perl could use them as string literals.

=item UCS

Short for I<Universal Character Set>.  When you say just UCS, it means
I<Unicode>

=item UCS-2

ISO/IEC 10646 encoding form: Universal Character Set coded in two
octets.

=item Unicode

A Character Set that aims to include all character repertoire of the
world.  Many character sets in various national as well as industrial
standards have become, in a way, just subsets of Unicode.

=item UTF

Short for I<Unicode Transformation Format>.  Determines how to map a
Unicode character into byte sequence.

=item UTF-16

A UTF in 16-bit encoding.  Can either be in big endian or little
endian.  Big endian version is called UTF-16BE (equals to UCS-2 + 
Surrogate Support) and little endian version is UTF-16LE.

=back

=head1 See Also

L<Encode>, 
L<Encode::Byte>, 
L<Encode::CN>, L<Encode::JP>, L<Encode::KR>, L<Encode::TW>,
L<Encode::EBCDIC>, L<Encode::Symbol>

=head1 References

=over 2

=item ECMA

European Computer Manufacturers Association
L<http://www.ecma.ch>

=over 2

=item EMCA-035 (eq C<ISO-2022>)

L<http://www.ecma.ch/ecma1/STAND/ECMA-035.HTM> 

The very specification of ISO-2022 is available from the link above.

=back

=item IANA

Internet Assigned Numbers Authority
L<http://www.iana.org/>

=over 2

=item Assigned Charset Names by IANA

L<http://www.iana.org/assignments/character-sets>

Most of the C<canonical names> in Encode derive from this list
so you can directly apply the string you have extracted from MIME
header of mails and web pages.

=back

=item ISO

International Organization for Standardization
L<http://www.iso.ch/>

=item RFC

Request For Comments -- need I say more?
L<http://www.rfc.net/>, L<http://www.faqs.org/rfcs/>

=item UC

Unicode Consortium
L<http://www.unicode.org/>

=over 2

=item Unicode Glossary

L<http://www.unicode.org/glossary/>

The glossary of this document is based upon this site.

=back

=back

=head2 Other Notable Sites

=over 2

=item czyborra.com

L<http://czyborra.com/>

Contains a a lot of useful information, especially gory details of ISO
vs. vendor mappings.

=item CJK.inf

L<http://www.oreilly.com/people/authors/lunde/cjk_inf.html>

Somewhat obsolete (last update in 1996), but still useful.  Also try

L<ftp://ftp.oreilly.com/pub/examples/nutshell/cjkv/pdf/GB18030_Summary.pdf>

You will find brief info on C<EUC-CN>, C<GBK> and mostly on C<GB 18030>

=item Jungshik Shin's Hangul FAQ

L<http://jshin.net/faq>

And especially it's subject 8.

L<http://jshin.net/faq/qa8.html>

A comprehensive overview of the Korean (C<KS *>) standards.

=back

=head2 Offline sources

=over 2

=item C<CJKV Information Processing> by Ken Lunde

CJKV Information Processing
1999 O'Reilly & Associates, ISBN : 1-56592-224-7

The modern successor of the C<CJK.inf>.

Features a comprehensive coverage on CJKV character sets and
encodings along with many other issues faced by anyone trying
to better support CJKV languages/scripts in all the areas of
information processing.

To purchase this book visit
L<http://www.oreilly.com/catalog/cjkvinfo/>

=back

=cut

I could not find this page because the hostname doesn't resolve!

Brief description for most of the mentioned CJK encodings
L<http://www.debian.org.ru/doc/manuals/intro-i18n/ch-codes.html>