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Web Encodings

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Revision as of 00:31, 9 September 2009 by Annevk (talk | contribs) (Safari: add some rough notes)

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My scratchpad for encoding related notes.


  • Document existing practices by describing for each browser
    • The list of supported encodings.
    • The list of supported labels for those encodings.
    • The matching algorithm for labels.
  • Converge the various used algorithms by
    • Defining a list of encodings everyone has to support. Browsers may not support more encodings than on that list.
    • Defining a list of supported labels for those encodings. Browsers may not support more labels than on that list.
    • Defining the matching algorithm. (HTML5 has been updated with a better one now.)
  • Get the new rules implemented

Documenting more exactly the encoding and decoding algorithms for each encoding and getting that implemented interoperably would also be great.

Current Implementations

Does this differ per platform? Opera might differ a bit on Mac.


Integrate this awesome data somehow:



UTS22 and strips leading x characters. (For now, plan is to switch to removing leading and trailing whitespace and ASCII case-insensitive matching afterwards in the future.)


Encoding Labels Decoded As Notes
big5 big5, cnbig5, csbig5
big5-hkscs big5hkscs
euc-jp cseucpkdfmtjapanese, eucjp, extendedunixcodepackedformatforjapanese
euc-kr cseuckr, csksc56011987, euckr, isoir149, korean, ksc5601, ksc56011987, ksc56011989, windows949
euc-tw euctw
gb18030 gb18030
gbk chinese, cngb, cp936, csgb2312, csiso58gb231280, euccn, gb2312, gb231280, gbk, isoir58, ms936, windows936
hz-gb-2312 hzgb2312
ibm866 866, cp866, csibm866, ibm866
iso-2022-cn iso2022cn
iso-2022-jp csiso2022jp, iso2022jp
iso-2022-jp-1 iso2022jp1
iso-2022-kr csiso2022kr, iso2022kr
iso-8859-1 cp819, csisolatin1, ibm819, iso88591, iso885911987, isoir100, l1, latin1 windows-1252
iso-8859-2 csisolatin2, iso88592, iso885921987, isoir101, l2, latin2
iso-8859-3 csisolatin3, iso88593, iso885931988, isoir109, l3, latin3
iso-8859-4 csisolatin4, iso88594, iso885941988, isoir110, l4, latin4
iso-8859-5 csisolatincyrillic, cyrillic, iso88595, iso885951988, isoir144
iso-8859-6 arabic, asmo708, csiso88596e, csisolatinarabic, ecma114, iso88596, iso885961987, iso88596e, isoir127
iso-8859-6-i csiso88596i, iso88596i
iso-8859-7 csisolatingreek, ecma118, elot928, greek, greek8, iso88597, iso885971987, isoir126
iso-8859-8 csiso88598e, csisolatinhebrew, hebrew, iso88598, iso885981988, iso88598e, isoir138, visual
iso-8859-8-i csiso88598i, iso88598i
iso-8859-9 csisolatin5, iso88599, iso885991989, isoir148, l5, latin5
iso-8859-10 csisolatin6, iso885910, iso8859101992, isoir157, l6, latin6
iso-8859-11 iso885911, tis620, tis6202533, windows874 Actually implemented as windows-874
iso-8859-13 iso885913
iso-8859-14 iso885914, iso8859141998, isoceltic, isoir199, l8, latin8
iso-8859-15 iso885915, latin9
iso-8859-16 iso885916, iso8859162001, isoir226, l10, latin10
koi8-r cskoi8r, koi8r
koi8-u koi8u
macintosh csmacintosh, mac, macintosh, macroman Likely disabled.
shift_jis cp932, csshiftjis, cswindows31j, ms932, mskanji, shiftjis, sjis, windows31j
tcvn tcvn, viettcvn
us-ascii ansix341968, ansix341986, ascii, cp367, csascii, csinvariant, csiso646basic1983, ibm367, invariant, iso646basic1983, iso646irv1991, iso646us, isoir6, ref, us, usascii windows-1252
utf-16 csunicode, csunicode11, csunicodeascii, iso10646j1, iso10646ucs2, iso10646ucsbasic, utf16
utf-16be utf16be
utf-16le utf16le
utf-8 utf8
viscii csviscii, viscii
windows-1250 cp1250, microsoftcp1250, windows1250
windows-1251 cp1251, microsoftcp1251, windows1251
windows-1252 cp1252, microsoftcp1252, windows1252
windows-1253 cp1253, microsoftcp1253, windows1253
windows-1254 cp1254, microsoftcp1254, windows1254
windows-1255 cp1255, microsoftcp1255, windows1255
windows-1256 cp1256, microsoftcp1256, windows1256
windows-1257 cp1257, microsoftcp1257, windows1257
windows-1258 cp1258, microsoftcp1258, windows1258
windows-sami-2 samiws2, windowssami2, ws2
x-mac-ce macce Likely disabled.
x-mac-cyrillic maccyrillic Likely disabled.
x-mac-greek macgreek Likely disabled.
x-mac-turkish macturkish Likely disabled.
x-vps vps



ASCII lowercasing.


Encoding Labels Decoded As Notes
armscii-8 armscii-8
Big5 big5, csbig5, x-x-big5, zh_tw-big5
Big5-HKSCS big5-hkscs
EUC-JP cseucjpkdfmtjapanese, euc-jp, x-euc-jp
EUC-KR 5601, csksc56011987, csueckr, euc-kr, iso-ir-149, korean, ks_c_5601-1989, ksc5601, ksc_5601 x-windows-949
gb18030 gb18030
GB2312 chinese, csgb2312, csiso58gb231280, gb2312, gb_2312, gb_2312-80, iso-ir-58, zh_cn.euc x-gbk
GEOSTD8 geostd8 Does not seem to work.
HZ-GB-2312 hz-gb-2312
IBM850 850, cp850, csIBM850, ibm850 csIBM850 not recognised.
IBM852 852, cp852, csIBM852, ibm852 csIBM852 not recognised.
IBM855 855, cp855, csIBM855, ibm855 csIBM855 not recognised.
IBM857 857, cp857, csIBM857, ibm857 csIBM857 not recognised.
IBM862 862, cp862, csIBM862, ibm862 csIBM862 not recognised.
IBM864 864, cp864, csIBM864, ibm-864, ibm864 csIBM864 not recognised.
IBM864i 864i, cp864i, csibm864i, ibm-864i, ibm864i
IBM866 866, cp-866, cp866, csIBM866, ibm866 csIBM866 not recognised.
ISO-2022-CN iso-2022-cn, iso-2022-cn-ext
ISO-2022-JP csiso2022jp, csiso2022jp2, iso-2022-jp, iso-2022-jp-2
ISO-2022-KR csiso2022kr, iso-2022-kr
ISO-8859-1 cp819, csisolatin1, ibm819, iso-8859-1, iso-ir-100, iso8859-1, iso88591, iso_8859-1, l1, latin1 windows-1252
ISO-8859-10 csisolatin6, iso-8859-10, iso-ir-157, iso8859-10, iso885910, l6, latin6
ISO-8859-11 iso-8859-11, iso8859-11, iso885911 windows-874
ISO-8859-13 iso-8859-13, iso8859-13, iso885913
ISO-8859-14 iso-8859-14, iso8859-14, iso885914
ISO-8859-15 iso-8859-15, iso8859-15, iso885915, iso_8859-15
ISO-8859-16 iso-8859-16
ISO-8859-2 csisolatin2, iso-8859-2, iso-ir-101, iso8859-2, iso88592, iso_8859-2, l2, latin2
ISO-8859-3 csisolatin3, iso-8859-3, iso-ir-109, iso8859-3, iso88593, iso_8859-3, l3, latin3
ISO-8859-4 csisolatin4, iso-8859-4, iso-ir-110, iso8859-4, iso88594, iso_8859-4, l4, latin4
ISO-8859-5 csisolatincyrillic, cyrillic, iso-8859-5, iso-ir-144, iso8859-5, iso88595, iso_8859-5
ISO-8859-6 arabic, asmo-708, csisolatinarabic, ecma-114, iso-8859-6, iso-ir-127, iso8859-6, iso88596, iso_8859-6
ISO-8859-6-E csiso88596e, iso-8859-6-e
ISO-8859-6-I csiso88596i, iso-8859-6-i
ISO-8859-7 csisolatingreek, ecma-118, elot_928, greek, greek8, iso-8859-7, iso-ir-126, iso8859-7, iso88597, iso_8859-7, sun_eu_greek
ISO-8859-8 csisolatinhebrew, hebrew, iso-8859-8, iso-ir-138, iso8859-8, iso88598, iso_8859-8, visual
ISO-8859-8-E csiso88598e, iso-8859-8-e
ISO-8859-8-I csiso88598i, iso-8859-8-i, iso-8859-8i
ISO-8859-9 csisolatin5, iso-8859-9, iso-ir-148, iso8859-9, iso88599, iso_8859-9, l5, latin5
ISO-IR-111 csiso111ecmacyrillic, ecma-cyrillic, iso-ir-111
KOI8-R koi8-r
KOI8-U koi8-u
Shift_JIS csshiftjis, ms_kanji, shift-jis, shift_jis, windows-31j, x-sjis
T.61-8bit csiso103t618bit, iso-ir-103, t.61, t.61-8bit
TIS-620 tis-620, tis620 windows-874
us-ascii 646, ansi_x3.4-1968, ascii, us-ascii windows-1252
UTF-16 utf-16 Recognized as BE or LE by BOM or byte sniffing
UTF-16BE csunicode, csunicode11, csunicodeascii, csunicodelatin1, iso-10646, iso-10646-j-1, iso-10646-ucs-2, iso-10646-ucs-basic, iso-10646-unicode-latin1, utf-16be, x-iso-10646-ucs-2-be
UTF-16LE utf-16le, x-iso-10646-ucs-2-le
UTF-32 utf-32 Recognized as BE or LE by BOM or byte sniffing
UTF-32BE iso-10646-ucs-4, utf-32be, x-iso-10646-ucs-4-be
UTF-32LE utf-32le, x-iso-10646-ucs-4-le
UTF-7 csunicode11utf7, unicode-1-1-utf-7, unicode-2-0-utf-7, utf-7, x-unicode-2-0-utf-7
UTF-8 unicode-1-1-utf-8, utf-8, utf8
VISCII csviscii, viscii
windows-1250 cp1250, windows-1250, x-cp1250
windows-1251 ansi-1251, cp1251, windows-1251, x-cp1251
windows-1252 cp1252, windows-1252, x-cp1252
windows-1253 cp1253, windows-1253, x-cp1253
windows-1254 cp1254, windows-1254, x-cp1254
windows-1255 cp1255, windows-1255, x-cp1255
windows-1256 cp1256, windows-1256, x-cp1256
windows-1257 cp1257, windows-1257, x-cp1257
windows-1258 cp1258, windows-1258, x-cp1258
windows-874 ibm874, windows-874
windows-936 windows-936
x-euc-tw cns11643, x-euc-tw, zh_tw-euc
x-gbk gbk, x-gbk
x-imap4-modified-utf7 x-imap4-modified-utf7
x-johab x-johab
x-mac-arabic x-mac-arabic
x-mac-ce x-mac-ce
x-mac-croatian x-mac-croatian
x-mac-cyrillic x-mac-cyrillic
x-mac-devanagari x-mac-devanagari
x-mac-farsi x-mac-farsi
x-mac-greek x-mac-greek
x-mac-gujarati x-mac-gujarati
x-mac-gurmukhi x-mac-gurmukhi
x-mac-hebrew x-mac-hebrew
x-mac-icelandic x-mac-icelandic
x-mac-roman csMacintosh, mac, macintosh, x-mac-roman csMacintosh not recognised.
x-mac-romanian x-mac-romanian
x-mac-turkish x-mac-turkish
x-mac-ukrainian x-mac-ukrainian
x-user-defined x-user-defined
x-viet-tcvn5712 x-viet-tcvn5712
x-viet-vps x-viet-vps
x-windows-949 ks_c_5601-1987, x-windows-949

Table generated from <http://mxr.mozilla.org/mozilla1.9.1/source/intl/uconv/src/charsetalias.properties> (corresponds to Firefox 3.5.2).

Aliases (used for parsing, apparently not for serialisation) are scattered around in a large number of files; cf. <http://mxr.mozilla.org/firefox/source/intl/uconv/ucvlatin/nsISO885911ToUnicode.cpp> for the mapping from ISO-8859-11 to windows-874.

8-bit encodings (excluding UTFs, CJK encodings and T.61) tested using <http://coq.no/X/charset5/tests8bit.html> (fail/pass should not be taken too seriously yet, especially not for more obscure encodings), Firefox version 3.5.1, OS X.

Bugs: Filed <https://bugzilla.mozilla.org/show_bug.cgi?id=512060> for the labels marked 'not recognised' in the table above since the lack of support for these is clearly accidental rather than deliberate (though it seems to suggest that these particular labels are not particularly widely used). In most other cases, research and deliberation will be needed to distinguish between bugs and features.



Internet Explorer


Strips leading and trailing whitespace and then does ASCII(?) case-insensitive matching. (Matches HTML5.)


Needs sorting out:





Apple’s reference <http://developer.apple.com/documentation/Carbon/Conceptual/ProgWithTECM/tecmgr_encnames/tecmgr_encnames.html#//apple_ref/doc/uid/TP40000932-CH204-TPXREF103> is incomplete or at least severely out of date even as a description of the Text Encoding Conversion Manager (TECM).

Querying TECM programmatically gives labels for more encodings, but the set of encodings does not match what Safari currently supports.

According to webkit/WebCore/platform/text/TextCodecICU.cpp, WebKit now uses ICU <http://site.icu-project.org/> with additional aliases (webkit/WebCore/platform/text/TextCodecICU.cpp), additional encodings (webkit/WebCore/platform/text/mac/mac-encodings.txt) possibly implemented using TECM at least on the Mac, a list of official IANA labels (webkit/WebCore/platform/text/mac/character-sets.txt) and probably a few more which I have not noticed.

ICU 4.2’s icu/source/data/mappings/convrtrs.txt or <http://demo.icu-project.org/icu-bin/convexp> lists encodings and labels not supported in Safari 4.0 on Leopard, and webkit/WebCore/platform/text/TextCodecICU.cpp mentions that Tiger included ICU 3.2.

Does encoding support in Safari depend on OS and OS version, and will Safari ultimately support everything in ICU 4.2? -- Windows comes with ICU but does not support some of the encodings the Mac edition does.

Integrate notes from othermaciej in http://krijnhoetmer.nl/irc-logs/whatwg/20090909 Also: http://trac.webkit.org/browser/trunk/WebCore/platform/text