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Network Working Group                                            HF. ZhuRequest for Comments: 1922                                    Tsinghua UCategory: Informational                                           DY. Hu                                                              Tsinghua U                                                                ZG. Wang                                                                    CITS                                                                 TC. Kao                                                                     III                                                              WCH. Chang                                                                     III                                                              M. Crispin                                                            U Washington                                                              March 1996Chinese Character Encoding for Internet MessagesStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard.  Distribution of this memo is   unlimited.Abstract   This memo describes methods of transporting Chinese characters in   Internet services which transport text, such as electronic mail   [RFC-822], network news [RFC-1036], telnet [RFC-854] and the World   Wide Web [RFC-1866].Introduction   As the use of Internet covers more and more Chinese people in the   world, the need has increased for the ability to send documents   containing Chinese characters on the Internet.  The methods described   in this document provide means of transporting existing Chinese   character sets as well as leaving space for future extension.   This document describes two encodings, ISO-2022-CN and   ISO-2022-CN-EXT.  These are designed with interoperability in mind   and are encouraged in this document for current Chinese interchange;   they are 7-bit, support both simplified and traditional characters   using both GB and CNS/Big5, and do not impose any unusual quoting   requirements on ASCII characters.   As important related issues, this document gives detailed   descriptions of the two encodings CN-GB and CN-Big5, and a brief   description of ISO/IEC 10646 [ISO-10646].  CN-GB and CN-Big5 areZhu, et al                   Informational                      [Page 1]

RFC 1922               Chinese Character Encoding             March 1996   currently used as the internal codes for Chinese documents.   ISO-10646 is the universal multi-octet character set defined by ISO;   we feel that in the future it may become the preferred technology for   Chinese documents and electronic mail when it is widely available.Specification1.    7-bit Chinese encodings: ISO-2022-CN and ISO-2022-CN-EXT1.1.  Description   ISO-2022-CN is based on ISO 2022 [ISO-2022], similar to earlier work   on ISO-2022-JP [RFC-1468] and ISO-2022-KR [RFC-1557] for the Japanese   and Korean languages respectively.  It is 7-bit, and supports both   simplified Chinese characters using GB 2312-80 [GB-2312] and   traditional Chinese characters using the first two planes of CNS   11643 [CNS-11643], as well as ASCII [ASCII] characters.   ISO-2022-CN-EXT is a superset of ISO-2022-CN that additionally   supports other GB character sets and planes of CNS 11643.   Since ISO-2022-CN and ISO-2022-CN-EXT are 7-bit encodings, they do   not require the 8-bit SMTP extensions.  ISO-2022-CN supports all the   Chinese characters that appear in Big5 [BIG5].1.2.  ISO-2022-CN   The starting code of ISO-2022-CN is ASCII.  ASCII and Chinese   characters are distinguished by designations (ESC sequences) and   shift functions.   Designations define the Chinese character sets used in the text.   There are three kinds of designations: SOdesignation, SS2designation   and SS3designation.   The SOdesignation is in the form ESC $ ) <F>, where <F> is the "final   character" assigned to the character set by ISO (refer to the ISO   registry [ISOREG] for more details).  The SS2designation is in the   form ESC $ * <F>, and the SS3designation is in the form ESC $ + <F>.   A designation overrides any previous designation for subsequent bytes   in the text.   There are four kinds of shifts: SI, SO, SS2 and SS3.  Shift functions   specify how to interpret the subsequent bytes.   The shift SI (one byte with hexadecimal value 0F) declares that   subsequent bytes are interpreted in ASCII.Zhu, et al                   Informational                      [Page 2]

RFC 1922               Chinese Character Encoding             March 1996   The shift SO (one byte with hexadecimal value 0E) declares that   subsequent bytes are interpreted in the character set defined by   SOdesignation.   The shift SS2 (two bytes with hexadecimal values 1B 4E) declares that   the subsequent TWO bytes are interpreted in the character set defined   by SS2designation, after which the previous interpretation (from SI   or SO) is restored.   The shift SS3 (two bytes with hexadecimal values 1B 4F) declares that   the subsequent TWO bytes are interpreted in the character set defined   by SS3designation, after which the previous interpretation (from SI   or SO) is restored.   The escape sequences, shift functions and character sets used in an   ISO-2022-CN text are as follows:    Character sets                                       Shift in with   --------------------------------------------------------------------     ASCII                                                     SI     GB 2312, CNS 11643-plane-1                                SO              CNS 11643-plane-2                                SS2      ESC $ ) A         Indicates the bytes following SO are Chinese                        characters as defined in GB 2312-80, until                        another SOdesignation appears      ESC $ ) G         Indicates the bytes following SO are as defined                        in CNS 11643-plane-1, until another                        SOdesignation appears      ESC $ * H         Indicates the two bytes immediately following                        SS2 is a Chinese character as defined in CNS                        11643-plane-2, until another SS2designation                        appears   If there are any GB or CNS characters on a line, a designation for   the corresponding character set must be used so that each line has   its own character set information and the text can be displayed   correctly when scroll back in a window.  Also, there must be a shift   to ASCII (SI) before the end of the line (i.e., before the CRLF).  In   other words, each line starts in ASCII, and ends in ASCII.      Example: the hex sequence         1b 24 29 41 0e 3d 3b 3b 3b 1b 24 29 47 47 28 5f 50 0f      represents the Chinese word for "Interchange" (jiao huan) twice;Zhu, et al                   Informational                      [Page 3]

RFC 1922               Chinese Character Encoding             March 1996      the first time in simplified form using GB-2312 (the 3d 3b 3b 3b      sequence above), and the second time in traditional form using      CNS-11643 (the 47 28 5f 50 sequence above).  The sequence 1b 24 29      41 is the SOdesignation for GB-2312, the 0e is SO to switch to      Chinese from ASCII, the 1b 24 29 47 is the SOdesignation for      CNS-11643 plane 1, and finally the 0f is the SI to return to ASCII      at the end of the line.   The name given to this character encoding is "ISO-2022-CN". This name   is intended to be used as the "charset" parameter in MIME [MIME-1,   MIME-2] messages.      Content-Type: text/plain; charset=iso-2022-cn   The ISO-2022-CN encoding is already in 7-bit form, so it is not   necessary to use a Content-Transfer-Encoding header.   Other restrictions are given in the "Formal Syntax of ISO-2022-CN"   (Section 7.1 of this document).1.3.  ISO-2022-CN-EXT   ISO-2022-CN-EXT supports all characters in existing GB, Big5 and CNS   11643 character sets.   The escape sequences, shift functions and character sets used in an   ISO-2022-CN-EXT text are as follows:    Character sets                                       Shift in with   --------------------------------------------------------------------     ASCII                                                    SI     GB 2312, GB 12345, CNS 11643-plane-1, ISO-IR-165         SO     GB 7589, GB 13131, CNS 11643-plane-2                     SS2     GB 7590, GB 13132 or other new GBs,CNS 11643-plane-3 or  SS3      higher planes of CNS 11643      Note: Currently, there are some GB sets that have not been      registered in ISO. Here <X7589>, <X7590>, <X12345>, <X13131> and      <X13132> represent the final character that will be assigned by      ISO for those sets.  These GB sets shall only be used once these      final characters are assigned.Zhu, et al                   Informational                      [Page 4]

RFC 1922               Chinese Character Encoding             March 1996      ESC $ ) A         Indicates the bytes following SO are Chinese                        characters as defined in GB 2312-80, until                        another SOdesignation appears      ESC $ * <X7589>   Indicates the two bytes immediately following                        SS2 is a Chinese character as defined in GB                        7589-87 [GB-7589], until another SS2designation                        appears      ESC $ + <X7590>   Indicates the two bytes immediately following                        SS3 is a Chinese character as defined in GB                        7590-87 [GB-7590], until another SS3designation                        appears      ESC $ ) <X12345>  Indicates the bytes following SO are as defined                        in GB 12345-90 [GB-12345], until another                        SOdesignation appears      ESC $ * <X13131>  Indicates the two bytes immediately following                        SS2 is a Chinese character as defined in GB                        13131-91 [GB-13131], until another                        SS2designation appears      ESC $ + <X13132>  Indicates the two bytes immediately following                        SS3 is a Chinese character as defined in GB                        13132-91 [GB-13131], until another                        SS3designation appears      ESC $ ) E         Indicates the bytes following SO are as defined                        in ISO-IR-165 (for details, seesection 2.1),                        until another SOdesignation appears      ESC $ ) G         Indicates the bytes following SO are as defined                        in CNS 11643-plane-1, until another                        SOdesignation appears      ESC $ * H         Indicates the two bytes immediately following                        SS2 is a Chinese character as defined in CNS                        11643-plane-2, until another SS2designation                        appears      ESC $ + I         Indicates the immediate two bytes following SS3                        is a Chinese character as defined in CNS                        11643-plane-3, until another SS3designation                        appearsZhu, et al                   Informational                      [Page 5]

RFC 1922               Chinese Character Encoding             March 1996      ESC $ + J         Indicates the immediate two bytes following SS3                        is a Chinese character as defined in CNS                        11643-plane-4, until another SS3designation                        appears      ESC $ + K         Indicates the immediate two bytes following SS3                        is a Chinese character as defined in CNS                        11643-plane-5, until another SS3designation                        appears      ESC $ + L         Indicates the immediate two bytes following SS3                        is a Chinese character as defined in CNS                        11643-plane-6, until another SS3designation                        appears      ESC $ + M         Indicates the immediate two bytes following SS3                        is a Chinese character as defined in CNS                        11643-plane-7, until another SS3designation                        appears   As in ISO-2022-CN, each line starts in ASCII, and ends in ASCII, and   has its own designation information before any Chinese characters   appear.   The name given to this character encoding is "ISO-2022-CN-EXT". This   name is intended to be used as the "charset" parameter in MIME   messages.      Content-Type: text/plain; charset=ISO-2022-CN-EXT   The ISO-2022-CN-EXT encoding is also in 7-bit form, so it is not   necessary to use a Content-Transfer-Encoding header.   Other restrictions are given in the "Formal Syntax of   ISO-2022-CN-EXT" (Section 7.2 of this document).1.4.  How to Support Big5 or other internal codesets with ISO-2022-CN      and ISO-2022-CN-EXT   Since there are many different Chinese internal coding systems   [CJKINF], such as EUC GB, Big5, CCCII (an encoding for library   systems mainly used in Taiwan), GBK (the new standard specification   for Chinese internal code, also is the codepage for Microsoft   simplified Chinese Windows 95) etc., ISO-2022-CN and ISO-2022-CN-EXT,   which are 7-bit and will not lose information during communication   among different codesets,  facilitate interchange between the various   Chinese coding systems in the Internet.Zhu, et al                   Informational                      [Page 6]

RFC 1922               Chinese Character Encoding             March 1996   For instance, ISO-2022-CN and ISO-2022-CN-EXT can be used to support   the popular Big5 codeset, because the first two planes of CNS-11643   contain the same Chinese characters as Big5's "common part" except   two duplicate characters.  By the "common part" we mean the part that   is not specific to any Big5 vendor, consisting of 5401 more   frequently used characters in Big5 range 0xA440-0xC67E, 7652 less   frequently used characters in Big5 range 0xC940-0xF9D5, and 441 other   symbols in Big5 range 0xA140-0xA3E0, as defined in Institute for   Information Industry's (III) technical report C-26 (see also [Big5]).   The appendix of this document presents a conversion table for   converting Big5 into CNS-11643, including specific extensions of some   popular vendors.  For other extensions, vendors and implementors of   Big5 products are ENCOURAGED to create detailed conversion tables, in   order to increase interoperability between different coding systems.   Public domain software (binary or C source code) for conversion   between Big5 and CNS-11643 is available on many Internet sites.  At   the time of this writing, the following FTP sites and software are   advertised:   1) Beijing:ftp://ftp.net.tsinghua.edu.cn/pub/Chinese/convert/big5cns.zip      (IP address: 166.111.1.6)   2) Xi'an:ftp://ftp.xanet.edu.cn/pub/chinese-soft/unix/convert/BeTTY-1.534.tar.gz      (IP address: 202.112.11.131)   3) Taiwan:ftp://ftp.seed.net.tw/Pub/Chinese/DOS/code-convert/chcode.zip      (IP address: 140.92.1.65)   4) US:ftp://ftp.ifcss.org/pub/software/unix/convert/BeTTY-1.534.tar.gz      (IP address: 128.123.1.55)   5) Japan:ftp://etlport.etl.go.jp/pub/iso-2022-cn/convert/big5cns.zip      (IP address: 192.31.197.99)Zhu, et al                   Informational                      [Page 7]

RFC 1922               Chinese Character Encoding             March 19962.    8-bit Chinese encodings: CN-GB and CN-Big5   The CN-GB and CN-Big5 MIME charsets are defined below.      Note: the use of 8-bit character sets requires the use of either      an 8-to-7 Content-Transfer-Encoding mechanism such as "BASE64" or      "QUOTED-PRINTABLE" if the network is not 8-bit clean, or the 8-bit      SMTP extensions [SMTPEXT] with the "8BIT"      Content-Transfer-Encoding on 8-bit clean networks.  Otherwise, an      8-bit message that passes through a 7-bit mailer is likely to have      the 8th bit truncated, resulting in an unreadable message.      Although "just send 8-bit data" has been common practice in the      past, it is incorrect according to the Internet standards and      causes interoperability problems.2.1.  CN-GB   E-mail using CN-GB characters is sent in this way:   GB 2312-80 characters are used with ASCII characters, not GB 1988-89   [GB-1988].   GB 2312-80 is also 7-bit, to avoid conflicting with ASCII.  If the   character is from GB 2312-80, the MSB (bit-8) of each byte is set to   1, and therefore becomes a 8-bit character.  Otherwise, the byte is   interpreted as ASCII.  This constructs a character set named "GB   Internal Code".   This method is also adopted in the .gb files in the Internet.   To use this character scheme with MIME, CN-GB is used as the value   for the charset parameter:      Content-Type: text/plain; charset=cn-gb; charset-edition=1980      Note: The "charset-edition" is a new MIME parameter described insection 4.1 of the "Specification" part of this document.   GB 12345-90 is the traditional form of GB 2312, the charset name   given to this set is CN-GB-12345 with the charset-edition of 1990.   There are also character sets that can only be used with other GB   sets.  For example, GB 8565-88 [GB-8565] is used with GB 2312 and   some other characters to form the ISO-IR-165 set (also known as GB   2312 + GB 8565.2).  ISO-IR-165 contains all characters from GB   2312-80 as revised by GB 6345.1-86 and GB 8565.2-88.  Its MIME   charset name is CN-GB-ISOIR165 with the charset-edition of 1992.Zhu, et al                   Informational                      [Page 8]

RFC 1922               Chinese Character Encoding             March 1996   CN-GB-12345 and CN-GB-ISOIR165 support ASCII in a similar manner to   CN-GB; the MSB of Chinese characters is set to 1 to distinguish from   ASCII.      Note: There are some supplementary character sets in GB, i.e.  GB      7589-87, GB 7590-87, GB 13131-91 and GB 13132-91.  Normally, they      won't be used independently without using GB-2312 or GB-12345, so      they are not necessarily to be registered.  Characters in these      standards could be supported with ISO-2022-CN and ISO-2022-CN-EXT.      If, in the future, they need to be used with "charset" names, it      is the responsibility of any interested third party (the      standardization organization or anybody else) to write the      necessary documents and register the charset with the IANA.  It is      encouraged that the charset names take the form of CN-GB-<number>,      such as CN-GB-12345, where <number> is the GB standard number.  A      charset-edition should also be given.  All CN-GB-<number> sets      should be coded in 8-bit in a similar fashion to CN-GB.   To ensure interoperability, the CN-GB charset should be used whenever   possible instead of a CN-GB-<number> charset.2.2.  CN-Big5   Big5 is a two-byte character set of traditional Chinese characters,   widely used in Taiwan and overseas.  E-mail of CN-Big5 is sent in   this way:   Big5 is used with ASCII.  The MSB of ASCII characters is always 0.   The MSB of the first byte of a Big5 character is always 1; this   distinguishes it from an ASCII character.  The second byte has 8   significant bits.  Therefore, CN-Big5 is an 8-bit encoding with a   15-bit codespace.   To use this character scheme with MIME, CN-Big5 is used as the value   for the charset parameter:      Content-Type: text/plain; charset=cn-big5; charset-edition=1984      Note: The "charset-edition" is a new MIME parameter described insection 4.1 of the "Specification" part of this document.3.    Universal Multilingual Character Set:ISO/IEC-10646/Unicode   ISO/IEC 10646 defines a 32bit character space with the intent to   encode all characters in the world. Currently, only the lowest 16bit   plane of ISO 10646, the Basic Multilingual Plane (BMP), is defined.   The BMP is code-by-code identical to Unicode [Unicode 1.1].  it   contains a large repertoire of Chinese characters (it currentlyZhu, et al                   Informational                      [Page 9]

RFC 1922               Chinese Character Encoding             March 1996   includes all the characters of GB 2312-80, GB 12345-90, GB 8565-89,   CNS 11643's plane 1 and 2, and part of some other standards) and   therefore can be used to transport Chinese characters in the Internet   community.  This document does not give any details on how to do   this, as this has been done elsewhere.  For details of using Unicode   with MIME, refer toRFC 1641 [RFC-1641],RFC 1642 [RFC-1642].  For   assigned names for 10646 set, refer to STD 2--"Assigned Numbers",   which isRFC 1700 [RFC-1700] currently.  For more up-to-date assigned   numbers, please check:ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets4.   Two New MIME parameters   Here we define two new MIME parameters to be used with "charset"   parameters.4.1.  "charset-edition"   This parameter is used after the MIME "charset" parameter, using four   digits (AD) to indicate what the year of edition is for the character   set standard shown in "charset".  Its use is optional.   Implementations should ignore this parameter unless the   implementation has specific support for that particular character set   edition.   The reason for defining this parameter is that there are often   differences in the defined characters between editions of a character   set standard.  Sometimes, the difference can not be ignored,   otherwise implementations would have problems when processing it.   There are only two ways to indicate this difference, in the current   MIME syntax.  One way is to indicate the edition in the charset name,   such as CN-GB-1988-80 (the 1980's edition of GB 1988).  The other way   is to define a new optional parameter such as "charset-edition".  The   latter way is better because receiving applications that can only   process an older edition can still recognize the character set and   offer to display the text in the older edition.  This display may   have a few mistakes, but it is better than refusing to display any   text at all or defaulting to an inappropriate character set such as   US-ASCII or ISO-8859-1.4.2.  "charset-extension"   This parameter is also used after the MIME "charset" parameter.  It   is case-insensitive and optional, and any value of this parameter   should be registered in IANA.  Unregistered value should start with   "x-" as with any MIME extension-token.  Implementations should ignore   this parameter unless the implementation has specific support forZhu, et al                   Informational                     [Page 10]

RFC 1922               Chinese Character Encoding             March 1996   that particular character set extension.   A character set extension has displayed glyphs for code points that   are not assigned in the character set, for example, vendor-specific   extensions of standard character sets.  This parameter provides the   option of using these extensions.  Although character set extensions   may cause interoperability problems, we recognize the existence of   such extensions.   For example:      Content-Type: text/plain; charset=CN-Big5; charset-edition=1984;       charset-extension=ETen-2.00.03-DOS   This may indicate Eten company's extension of Big5: ETen 2.00.03 for   DOS, assuming that "ETen-2.00.03-DOS" is registered with the IANA..4.3.  Formal Syntax:   The following changes and additions are made to the MIME syntax:   charset-edition   := "charset-edition" "=" 4DIGIT                         ; year of edition in four digits   charset-extension := "charset-extension" "=" extension-token5.   Background Information5.1. Writing systems and their encodings in Chinese-speaking nations and     regions   The mainland provinces of China use simplified Chinese character in   daily life.  GB is the standard electronic character set.  It is the   main means for communications between people who share simplified   Chinese characters in the world.   Taiwan uses traditional Chinese characters in daily life.  CNS-11643   is the formal character set for information interchange in Taiwan;   however, Big5, a widely-used character set of traditional Chinese   characters, is the de-facto internal code standard in Taiwan.   Hong Kong uses traditional Chinese characters in daily life, but uses   both GB and Big5 in electronic form, because Hong Kong people often   communicate with people in all of China's provinces.   Singapore seldom uses Chinese characters, and uses the simplified   form when Chinese characters are used.  In electronic form, Unicode   is more popular, however GB is also used.Zhu, et al                   Informational                     [Page 11]

RFC 1922               Chinese Character Encoding             March 19965.2.  Miscellaneous information about Chinese character sets   The GB 1988-89 character set is identical to ISO 646 [ISO-646] except   for currency symbol and tilde. The currency symbol and the tilde are   replaced by the Yuan sign and the overline.  This set is GB's variant   of ISO 646.  This character set and CNS 5205 [CNS-5205] are not   encouraged for use in the Internet, since ASCII combined with GB 2312   or CNS 11643-plane 1 and plane 2 contains all the characters in them.   The GB 2312-80 character set consists of simplified Chinese   characters, digits, and the Latin, Greek and Russian alphabets, and   some other symbols; in all, 7445 characters.  Each character is   represented with two bytes.   GB 13000-95 [GB-13000] is GB's variant of ISO 10646.  However, for   interoperability in the Internet, assigned names for ISO 10646 are   encouraged instead.   Currently both sides of the Taiwan Straits are cooperating closely in   promoting the use of ISO 10646's BMP and in continuing its   development together with other organizations under ISO.5.3.  Miscellaneous implementation information   For maximum interoperability, implementations SHOULD at least support   sending and receiving ISO-2022-CN.  Supporting all registered   character sets in ISO-2022-CN-EXT is greatly encouraged.   To meet the current usage, support of CN-GB (the status quo for   simplified Chinese e-mail ) or CN-Big5 (the status quo for   traditional Chinese e-mail) may be necessary.  However, it is not   reliable to send documents directly with these internal codes,   therefore sending ISO-2022-CN message is always encouraged whenever   possible.   To the maximum extent possible, implementations should be capable of   receiving messages in any of the encodings described in this   document, even if they only transmit messages in one form.   Preferably the implementation should display the characters with   glyphs appropriate to the typographic tradition that is implied in   the encoding of the received text.  Implementation may also translate   these encodings to the encoding that its platform supports.   The human user (not implementor) should try to keep lines within 80   display columns, or, preferably, within 75 (or so) columns, to allow   insertion of ">" at the beginning of each line in excerpts.  Each   Chinese character takes up two columns, and the shift sequences doZhu, et al                   Informational                     [Page 12]

RFC 1922               Chinese Character Encoding             March 1996   not take up any columns.  The implementor is reminded that Chinese   characters take up two bytes and should not be split in the middle to   break lines for displaying, etc.   Freely available fonts of Chinese characters:      Beijing:ftp://ftp.net.tsinghua.edu.cn/pub/Chinese/fonts/      Xi'an:ftp://ftp.xanet.edu.cn/pub/chinese-soft/fonts/      Taiwan:ftp://ftp.edu.tw/Chinese/ifcss/software/fonts/ftp://ftp.ntu.edu.tw/Chinese/ifcss/software/fonts/      Hong Kong:ftp://ftp.cuhk.hk/pub/chinese/ifcss/software/fonts/      Singapore:ftp://ftp.technet.sg:/pub/chinese/fonts/      US:ftp://ftp.ifcss.org/pub/software/fonts/http://ccic.ifcss.org/www/pub/software/fonts/6.   X.400 Considerations   X.400 has the ability of carrying different character sets in a   message by using the body part "GeneralText" defined by   ISO/IEC-10021-7 [ISO-10021].   The X.400 ASN.1 definition of the GeneralText body part is:    general-text-body-part EXTENDED-BODY-PART-TYPE      PARAMETERS GeneralTextParameters IDENTIFIED BY id-ep-general-text      DATA       GeneralTextData      ::= id-et-general-text    GeneralTextParameters ::= SET OF CharacterSetRegistration    CharacterSetRegistration ::= INTEGER (1..32767)    GeneralTextData ::= GeneralString   Therefore, to use ISO-2022-CN, set the "CharacterSetRegistration"   part as { 6 58 171 172 }, and add an ESC sequence of ESC ( B (three   bytes, hexadecimal values: 1B 28 42) before the beginning of eachZhu, et al                   Informational                     [Page 13]

RFC 1922               Chinese Character Encoding             March 1996   line of ISO-2022-CN text.   Similarly, to use ISO-2022-CN-EXT, set the registered numbers of all   character sets in the "CharacterSetRegistration" part and add ESC ( B   at the beginning of each line.  For the registered numbers, please   refer to ISO registry.  In addition to the character sets supported   by ISO-2022-CN, currently registered numbers are:      ISO IR 165 (GB 2312+GB 8565.2):   165      CNS 11643-plane 3:                183      CNS 11643-plane 4:                184      CNS 11643-plane 5:                185      CNS 11643-plane 6:                186      CNS 11643-plane 7:                187   176 is the registered number for the BASESET of ISO/IEC 10646-1:1993   UCS-2 with implementation level 3, Escape sequence of ESC % / E (four   bytes, hexadecimal values 1B 25 2F 45) indicates starting of this   codeset.   For CN-GB and CN-Big5 character sets, there are no formal methods   that could be used in X.400 yet.   For detail about X.400 use of character sets, please refer toRFC1502 [RFC-1502].Zhu, et al                   Informational                     [Page 14]

RFC 1922               Chinese Character Encoding             March 19967.   Formal Syntax of ISO-2022-CN and ISO-2022-CN-EXT   The notational conventions used here are identical to those used inRFC 822.7.1.  Formal Syntax of ISO-2022-CN   body  ::= * ( ascii_line / c_line )   ascii_line  ::= *char CRLF   c_line ::= *char 1*(1*designation 1*(*char 1*c_text *char)) CRLF   designation  ::= SOdesignation / SS2designation   SOdesignation  ::= ESC "$" ")" finalchar_for_SO   SS2designation  ::= ESC "$" "*" finalchar_for_SS2   finalchar_for_SO  ::= "A" / "G"   finalchar_for_SS2  ::= "H"   c_text  ::= 1* ( SO-SI-segment / SS2segment )   SO-SI-segment ::= SO 1*c_char *designation *c_segment SI   c_segment  ::= 1* ( c_char / SS2segment )   SS2segment  ::= SS2 c_char   c_char  ::= one_of_94  one_of_94                                                   ; ( Octal, Decimal.)   ESC             ::= <ISO-646 ESC, escape>       ; ( 33, 27.)   SI              ::= <ASCII SI, shift in>        ; ( 17, 15.)   SO              ::= <ASCII SO, shift out>       ; ( 16, 14.)   SS2             ::= <ISO 2022 Single_shift two> ; ( 33 116, 27 78.)   one_of_94       ::= <any char in 94_char set>   ; ( 41-176, 33-126. )   char            ::= <any char in 96_char_set>   ; ( 40-177, 30-127. )Zhu, et al                   Informational                     [Page 15]

RFC 1922               Chinese Character Encoding             March 19967.2.  Formal Syntax of ISO-2022-CN-EXT   body  ::= * ( ascii_line / c_line )   ascii_line  ::= *char CRLF   c_line ::= *char 1*(1*designation 1*(*char 1*c_text *char)) CRLF   designation  ::= SOdesignation / SS2designation / SS3designation   SOdesignation  ::= ESC "$" ")" finalchar_for_SO   SS2designation  ::= ESC "$" "*" finalchar_for_SS2   SS3designation  ::= ESC "$" "+" finalchar_for_SS3   finalchar_for_SO  ::= "A" / <X12345> / "G" / "E"   finalchar_for_SS2  ::= <X7589> / <X13131> / "H"   finalchar_for_SS3  ::= <X7590> / <X13132> / "I" / "J" / "K" / "L"                          / "M"   c_text  ::= 1* ( SO-SI-segment / SS2segment / SS3segment )   SO-SI-segment ::= SO 1*c_char *designation *c_segment SI   c_segment  ::= 1* ( c_char / SS2segment / SS3segment )   SS2segment  ::= SS2 c_char   SS3segment  ::= SS3 c_char   c_char  ::= one_of_94  one_of_94                                                    ; ( Octal, Decimal.)   ESC             ::= <ISO-646 ESC, escape>        ; ( 33, 27.)   SI              ::= <ASCII SI, shift in>         ; ( 17, 15.)   SO              ::= <ASCII SO, shift out>        ; ( 16, 14.)   SS2             ::= <ISO 2022 Single_shift two>  ; ( 33 116, 27 78.)   SS3             ::= <ISO 2022 Single_shift three>; ( 33 117, 27 79.)   one_of_94       ::= <any char in 94_char set>    ; ( 41-176, 33-126.Zhu, et al                   Informational                     [Page 16]

RFC 1922               Chinese Character Encoding             March 1996   )   char            ::= <any char in 96_char_set>    ; ( 40-177, 30-127.   )8.    Registration of New "charset"s and New MIME parameter8.1.  This document defines the following MIME "charset" names for      Chinese text:      ISO-2022-CN, ISO-2022-CN-EXT      CN-GB, CN-Big5      CN-GB-12345      CN-GB-ISOIR1658.2.  This document defines two new MIME parameters:      charset-edition      charset-extensionAcknowledgments   This document is the result of cooperation in APNG-CC, the Chinese   Character sub-working group of the I18N/L10N (Internationalization   and Localization) working group of APNG (Asia-Pacific Networking   Group), coordinator Zhu Haifeng <zhf@net.tsinghua.edu.cn>.  The   membership of APNG-CC consists of individuals from both sides of the   Taiwan Strait, HongKong, and from Singapore and other countries.  We   wish to thank all members of APNG-CC.   Prof. Yao Shiquan (Deputy chair of CITS--China Information Technology   Standardization Technical Committee), Ms. Lin Ning (Secretary-General   of CITS), Mr. Guo Chengzhong of the Office of the Joint Conference of   China Economic Information,  and Prof. Zhao Jingrong, Prof. Wu   Jianping, Prof. Li Xing, and Mr. You Yue (Tsinghua University) and   other experts from CERNET Expert Committee, Prof. Meng Qingyu (China   Computer Software & Technology Services Corporation), Prof. Cao   Jinwen and Mr. Yu Jun (IBM Beijing) gave a lot of support and help in   many aspects.   Special thanks for the supports towards APNG-CC from Prof. Yang   Tianxing (Chair of CITS).   Prof. Ding ZyKaan from Academia Sinica of Taiwan, and Mr. C. J.   Cherng and Mr. C. K. Fan of III (Institute for Information Industry),   Mr. Chang JingShin from Tsinghua University in Hsinchu of Taiwan, Ms.   C. C. Hsu from IBM Taiwan and  Ms. Tong-Lee Anita Lin from MicrosoftZhu, et al                   Informational                     [Page 17]

RFC 1922               Chinese Character Encoding             March 1996   Taiwan gave a lot of support and contributions in APNG-CC's work.  In   particular, Ms. C. C. Hsu put much effort towards completing the   Appendix of this document.   We also wish to thank the following people who contributed in many   ways towards this document.      Zhang Zhoucai              Martin J. Duerst      Zhang Ling                 Kenichi Handa      Zhu Bin                    Lu Chin      Sun Yufang                 Nelson Chin      Chen Shuyi                 Mao Yonggang      Masataka Ohta              Ken Lunde      Lua Kim Teng               Victor Cheng      Stephen G. Simpson         Yuan Jiang      Liu Huifang                Harald T. Alvestrand      Qian Hualin                Jiang Lin      Lu Ming                    Emily Hsu      Wu Jian                    Zhu Shuang      Zheng Long                 Zhang Hailin      Yonggang Zhang             Feng Hui      Yao JianSecurity Considerations   Security issues are not discussed in this memo.Authors' Addresses   Zhu Haifeng  (HF. Zhu)   216 Central Main Building   Tsinghua University   Beijing, 100084   China   Tel: +86-10-2561144 ext. 3492   Fax: +86-10-2564173   EMail: zhf@net.tsinghua.edu.cn, zhf@net.edu.cnZhu, et al                   Informational                     [Page 18]

RFC 1922               Chinese Character Encoding             March 1996   Hu Daoyuan  (DY. Hu)   Tsinghua Networking Center   Tsinghua University   Beijing, 100084   China   Tel: +86-10-2594016   Fax: +86-10-2564173   EMail: hdy@tsinghua.edu.cn   Wang Zhiguan  (ZG. Wang)   Beijing 1101 MailBox   SubCommitte 2 (SC2)   China Information Technology Standardization Technical Committee   (CITS)   Beijing, 100007   China   Tel: +86-10-4012392   Fax: +86-10-4010601   Kao Tien-cheu (TC. Kao)   I.T. Promotion Division   Institute for Information Industry (III)   Taipei   Taiwan   Tel: +886-2-5631688   Fax: +886-2-563-4209   EMail: tckao@iiidns.iii.org.tw   Chang Wen-chung  (WCH. Chang)   Institute for Information Industry (III)   Taipei   Taiwan   Tel: +886-2-7327771   Fax: +886-2-7370188   EMail: chung@iiidns.iii.org.twZhu, et al                   Informational                     [Page 19]

RFC 1922               Chinese Character Encoding             March 1996   Mark R. Crispin   Networks and Distributed Computing   University of Washington   4545 15th Avenue NE   Seattle, WA  98105-4527   USA   Tel: +1 (206) 543-5762   Fax: +1 (206) 685-4045   EMail: MRC@CAC.Washington.EDUZhu, et al                   Informational                     [Page 20]

RFC 1922               Chinese Character Encoding             March 1996Appendix -- Conversion Table for ISO-2022-CN (EXT) and Big5   This is a conversion table for the Chinese characters in Big5's   common part and ISO-2022-CN/-EXT, including all the vendor-specific   characters from Eten, Microsoft and IBM.  For conversion source and   binary programs for Big5, III provides good on-line services (ftp   site listed insection 1.4), and [CJKINF] is also a good reference.A.1.  Big5 (ETen, IBM, and Microsoft version) symbol set correspondence      to CNS 11643 Plane 1:      0xA140-0xA1F5 <-> 0x2121-0x2256             0xA1F6 <-> 0x2258             0xA1F7 <-> 0x2257      0xA1F8-0xA2AE <-> 0x2259-0x234E      0xA2AF-0xA3BF <-> 0x2421-0x2570      0xA3C0-0xA3E0 <-> 0x4221-0x4241 (ETen and Microsoft                                       defined as reserved area)A.2.  Big5 (ETen, IBM, and Microsoft version) Level 1 correspondence to      CNS 11643-1992 Plane 1:      0xA440-0xACFD <-> 0x4421-0x5322             0xACFE <-> 0x5753      0xAD40-0xAFCF <-> 0x5323-0x5752      0xAFD0-0xBBC7 <-> 0x5754-0x6B4F      0xBBC8-0xBE51 <-> 0x6B51-0x6F5B             0xBE52 <-> 0x6B50      0xBE53-0xC1AA <-> 0x6F5C-0x7534      0xC1AB-0xC2CA <-> 0x7536-0x7736             0xC2CB <-> 0x7535      0xC2CC-0xC360 <-> 0x7737-0x782C      0xC361-0xC3B8 <-> 0x782E-0x7863             0xC3B9 <-> 0x7865             0xC3BA <-> 0x7864      0xC3BB-0xC455 <-> 0x7866-0x7961             0xC456 <-> 0x782D      0xC457-0xC67E <-> 0x7962-0x7D4BA.3.  Big5 (ETen, IBM, and Microsoft version) Level 2 correspondence to      CNS 11643-1992 Plane 2:      0xC940-0xC949 <-> 0x2121-0x212A             0xC94A <-> 0x4442       # duplicate of Level 1's 0xA461      0xC94B-0xC96B <-> 0x212B-0x214B      0xC96C-0xC9BD <-> 0x214D-0x217C             0xC9BE <-> 0x214C      0xC9BF-0xC9EC <-> 0x217D-0x224CZhu, et al                   Informational                     [Page 21]

RFC 1922               Chinese Character Encoding             March 1996      0xC9ED-0xCAF6 <-> 0x224E-0x2438             0xCAF7 <-> 0x224D      0xCAF8-0xD779 <-> 0x2439-0x387D             0xD77A <-> 0x3F6A      0xD77B-0xDBA6 <-> 0x387E-0x3F69      0xDBA7-0xDDFB <-> 0x3F6B-0x4423             0xDDFC <-> 0x4176         # duplicate of 0xDCD1      0xDDFD-0xE8A2 <-> 0x4424-0x554A      0xE8A3-0xE975 <-> 0x554C-0x5721      0xE976-0xEB5A <-> 0x5723-0x5A27      0xEB5B-0xEBF0 <-> 0x5A29-0x5B3E             0xEBF1 <-> 0x554B      0xEBF2-0xECDD <-> 0x5B3F-0x5C69             0xECDE <-> 0x5722      0xECDF-0xEDA9 <-> 0x5C6A-0x5D73      0xEDAA-0xEEEA <-> 0x5D75-0x6038             0xEEEB <-> 0x642F      0xEEEC-0xF055 <-> 0x6039-0x6242             0xF056 <-> 0x5D74      0xF057-0xF0CA <-> 0x6243-0x6336             0xF0CB <-> 0x5A28      0xF0CC-0xF162 <-> 0x6337-0x642E      0xF163-0xF16A <-> 0x6430-0x6437             0xF16B <-> 0x6761      0xF16C-0xF267 <-> 0x6438-0x6572             0xF268 <-> 0x6934      0xF269-0xF2C2 <-> 0x6573-0x664C      0xF2C3-0xF374 <-> 0x664E-0x6760      0xF375-0xF465 <-> 0x6762-0x6933      0xF466-0xF4B4 <-> 0x6935-0x6961             0xF4B5 <-> 0x664D      0xF4B6-0xF4FC <-> 0x6962-0x6A4A      0xF4FD-0xF662 <-> 0x6A4C-0x6C51             0xF663 <-> 0x6A4B      0xF664-0xF976 <-> 0x6C52-0x7165      0xF977-0xF9C3 <-> 0x7167-0x7233             0xF9C4 <-> 0x7166             0xF9C5 <-> 0x7234             0xF9C6 <-> 0x7240      0xF9C7-0xF9D1 <-> 0x7235-0x723F      0xF9D2-0xF9D5 <-> 0x7241-0x7244A.4.  Big5 (ETen and IBM Version) specific numeric symbols      correspondence to CNS 11643 Plane 1: (Microsoft version defined      this area as UDC - User Defined Character)Zhu, et al                   Informational                     [Page 22]

RFC 1922               Chinese Character Encoding             March 1996      0xC6A1-0xC6BE <-> 0x2621 - 0x263EA.5.  Big5 (ETen and IBM Version) specific KangXi radicals      correspondence to CNS 11643 Plane 1: (Microsoft version defined as      UDC - User Definable Character)             0xC6BF <-> 0x2723             0xC6C0 <-> 0x2724             0xC6C1 <-> 0x2726             0xC6C2 <-> 0x2728             0xC6C3 <-> 0x272D             0xC6C4 <-> 0x272E             0xC6C5 <-> 0x272F             0xC6C6 <-> 0x2734             0xC6C7 <-> 0x2737             0xC6C8 <-> 0x273A             0xC6C9 <-> 0x273C             0xC6CA <-> 0x2742             0xC6CB <-> 0x2747             0xC6CC <-> 0x274E             0xC6CD <-> 0x2753             0xC6CE <-> 0x2754             0xC6CF <-> 0x2755             0xC6D0 <-> 0x2759             0xC6D1 <-> 0x275A             0xC6D2 <-> 0x2761             0xC6D3 <-> 0x2766             0xC6D4 <-> 0x2829             0xC6D5 <-> 0x282A             0xC6D6 <-> 0x2863             0xC6D7 <-> 0x286CA.6.  Big5 (ETen and Microsoft version) specific Ideographs      correspondence to CNS 11643 Plane 3: (IBM version defined as UDC)             0xF9D6 <-> 0x4337             0xF9D7 <-> 0x4F50             0xF9D8 <-> 0x444E             0xF9D9 <-> 0x504A             0xF9DA <-> 0x2C5D             0xF9DB <-> 0x3D7E             0xF9DC <-> 0x4B5CA.7.  Big5 (ETen version only) specific symbols correspondence to CNS      11643 Plane 4:             0xC879 <-> 0x2123Zhu, et al                   Informational                     [Page 23]

RFC 1922               Chinese Character Encoding             March 1996             0xC87B <-> 0x2124             0xC87D <-> 0x212A             0xC8A2 <-> 0x2152A.8.  Other Big5 specific symbols which cannot mapping to CNS 11643:      0xC6D8-0xC878 <-> none  (ETen and IBM Version)             0xC87A <-> none  (ETen version only)             0xC87C <-> none  (ETen version only)      0xC87E-0xC8A1 <-> none  (ETen version only)      0xC8A3-0xC8CC <-> none  (ETen version only)      0xC8CD-0xC8D3 <-> none  (ETen and IBM version)      0xF9DD-0xF9FE <-> none  (ETen and Microsoft version)      Note: However, most of them can be mapped to GB-2312 too.  For      example, Big5(ETen and IBM version) Hiragana, Katakana, and      Cyrillic symbols correspondence to GB-2312:      0xC6E7-0xC77A <-> 0x2421-0x2473  # Japanese Hiragana      0xC77B-0xC7F2 <-> 0x2521-0x2576  # Japanese Katakana      0xC7F3-0xC854 <-> 0xA7A1-0xA7C1  # Cyrillic uppercase      0xC855-0xC875 <-> 0xA7D1-0xA7F1  # Cyrillic lowercase   Please notice that there are also many symbols that could be   supported by GB-2312, for detail, please refer to the ftp sites insection 1.4 of the "Specification" part of this document.Zhu, et al                   Informational                     [Page 24]

RFC 1922               Chinese Character Encoding             March 1996References   [ASCII] American National Standards Institute, "Coded character set:   7-bit American National Standard Code for Information Interchange",   ANSI X3.4-1986.   [BIG5] Institute for Information Industry, "Chinese Coded Character   Set in Computer ", March, 1984   [CJKINF] Ken Lunde, On-line documentation of Chinese/Japanese/Korean   Information Processing, 1995, available at:ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf   [CNS-5205] "Information processing: 7-Bit Coded Character Set For   Information Interchange", CNS-5205.   [CNS-11643] "Chinese Standard Interchange Code", CNS-11643 version   1992; "Standard Interchange Code for Generally-Used Chinese   Characters", CNS 11643 version 1986.   [GB-1988] "7-bit Coding Character Set for Information Interchange",   GB 1988-89.   [GB-2312] "Coding of Chinese Ideogram Set for Information Interchange   Basic Set", GB 2312-80.   [GB-7589] "Code of Chinese Ideograms Set for Information Interchange,   the 2nd Supplementary Set", UDC 681.3.048, GB 7589-87.   [GB-7590] "Code of Chinese Ideogram Set for Information Interchange,   the 4th Supplementary Set", UDC 681.3.048, GB 7590-87.   [GB-8565] "Information Processing Coded Character Sets for Text   Communication", UDC 681.3, GB 8565-88.   [GB-12345] "Code of Chinese Ideogram Set for Information Interchange   Supplementary Set", GB/T 12345-90.   [GB-13000]  "Information Technology: Universal Multiple-Octet Coded   Character Set(UCS) Part 1: Architecture and Basic Multilingual   Plane", GB13000.1   [GB-13131] "Code of Chinese Ideogram Set for Information Interchange,   the 3rd Supplementary Set", GB 13131-91.   [GB-13132] "Code of Chinese Ideogram Set for Information Interchange,   the 5th Supplementary Set", GB 13132-91.Zhu, et al                   Informational                     [Page 25]

RFC 1922               Chinese Character Encoding             March 1996   [ISO-646] International Organization for Standardization (ISO),   "Information Technology: ISO 7-bit Coded Character Set for   Information Interchange", International Standard, Ref. No. ISO/IEC   646:1991.   [ISO-2022] International Organization for Standardization (ISO),   "Information Processing: ISO 7-bit and 8-bit coded character sets:   Code extension techniques", International Standard, Ref. No. ISO   2022-1986 (E).   [ISO-10021] Information Technology: Text communication:   Message-Oriented Text Interchange Systems (MOTIS), ISO 10021, October   1988.   [ISO-10646] ISO/IEC 10646-1:1993(E) Information Technology: Universal   Multiple-octet Coded Character Set (UCS) Part 1: Architecture and   Basic Multilingual Plane"   [ISOREG] International Organization for Standardization (ISO),   "International Register of Coded Character Sets To Be Used With   Escape Sequences".   [MIME-1] Borenstein, N., and Freed, N., "MIME (Multipurpose Internet   Mail Extensions) Part One: Mechanisms for Specifying and Describing   the Format of Internet Message Bodies",RFC 1521, Bellcore, Innosoft,   September 1993.   [MIME-2] Moore, K., "MIME (Multipurpose Internet Mail Extensions)   Part Two: Message Header Extensions for Non-ASCII Text",RFC 1522,   University of Tennessee, September 1993.   [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text   Messages", STD 11,RFC 822, University of Delaware, August 1982.   [RFC-854] Postel, J., Reynolds J., Telnet Protocol Specification,RFC854, ISI, May 1983.   [RFC-1036] Horton, M., and Adams, R., "Standard for Interchange of   USENET Messages",RFC 1036, AT&T Bell Laboratories, Center for   Seismic Studies, December 1987.   [RFC-1468] Murai J., Crispin, M., and van der Poel, E., Japanese   Character Encoding for Internet Messages, June 1993.   [RFC-1557] Choi U., Chon K., and Park H., Korean Character Encoding   for Internet Messages, December 1993.Zhu, et al                   Informational                     [Page 26]

RFC 1922               Chinese Character Encoding             March 1996   [RFC-1641] Goldsmith D., and Davis M., "Using Unicode with MIME",RFC1641, Taligent Inc., July 1994   [RFC-1642] Goldsmith D., and Davis M.," UTF-7, A Mail-Safe   Transformation Format of Unicode", July 1994   [RFC-1700] Reynolds J., and Postel J., "Assigned Numbers",RFC 1700,   STD 2, ISI, October 1994   [SMTP] Postel, J. B. "Simple Mail Transfer Protocol", STD 10,RFC821, USC/Information Sciences Institute, August 1982.   [SMTPEXT] Klensin J., Freed N., Rose M., Stefferud E., and Crocker   D., "SMTP Service Extensions",RFC 1651, July 1994.   [Unicode 1.1] "The Unicode Standard, Version 1.1", Addison-Wesley,   Reading, MA (to be published; the contents of this standard is   currently available by combining [Unicode92], [Unicode93], and   [Unicode4]).   [Unicode92] The Unicode Consortium, "The Unicode Standard: Worldwide   Character Encoding: Version 1.0", Volume 1, Addison-Wesley, Reading,   MA, 1992 (ISBN 0-201-56788-1).   [Unicode93] The Unicode Consortium, "The Unicode Standard: Worldwide   Character Encoding: Version 1.0", Volume 2, Addison-Wesley, Reading,   MA, 1992 (ISBN 0-201-60845-6).   [Unicode4] The Unicode Consortium, "The Unicode Standard: Version 1.1   (Prepublication Edition)", Unicode Technical Report #4 (avaliable   from the Unicode Consortium).Zhu, et al                   Informational                     [Page 27]