Japanese Character Encoding for Internet Messages
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 1468.
|Authors||Erik M. van der Poel , Mark Crispin , Dr. Jun Murai Ph.D.|
|Last updated||2013-03-02 (Latest revision 1993-01-18)|
|RFC stream||Internet Engineering Task Force (IETF)|
|IESG||IESG state||RFC 1468 (Informational)|
|Send notices to||(None)|
Network Working Group Jun Murai Internet Draft Mark Crispin Erik van der Poel 1st December 1992 Japanese Character Encoding for Internet Message Bodies Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any other Internet Draft. This draft document will be submitted to the RFC editor as an informational document. This document will expire before 1st June 1993. Distribution of this memo is unlimited. Please send comments to email@example.com. Introduction This document describes the encoding used in electronic mail [RFC822] and network news [RFC1036] message bodies in several Japanese networks. It was first specified by and used in JUNET [JUNET]. The encoding is now also widely used in Japanese IP communities. This document names the encoding "ISO-2022-JP", which is intended to be used in the "charset" parameter field of MIME [MIME] messages. The use of ISO-2022-JP in RFC 1342 [RFC1342] headers is expected to be the subject of a separate document. This document only describes the encoding of plain text. The encoding of other subtypes of text, such as richtext, is not discussed here. Murai et al Expires 1st June 1993 [Page 1] Internet Draft Updated 1st December 1992 Description The message body starts in ASCII [ASCII], and switches to Japanese characters through an escape sequence. For example, the escape sequence ESC $ B (three bytes, hexadecimal values: 1B 24 42) indicates that the bytes following this escape sequence are Japanese characters, which are encoded in two bytes each. To switch back to ASCII, the escape sequence ESC ( B is used. The following table gives the escape sequences and the character sets used in ISO-2022-JP messages. The ISOREG number is the registration number in ISO's registry [ISOREG]. Esc Seq Character Set ISOREG ESC ( B ASCII 6 ESC ( J JIS X 0201-1976 ("Roman" set) 14 ESC $ @ JIS X 0208-1978 42 ESC $ B JIS X 0208-1983 87 Note that JIS X 0208-1983 was called JIS C 6226-1983 until the name was changed in March 1987. Likewise, JIS C 6220 was renamed JIS X 0201. The "Roman" character set of JIS X 0201 [JISX0201] is identical to ASCII except for backslash (\) and tilde (~). The backslash is replaced by the Yen sign, and the tilde is replaced by macron (overline). This set is Japan's national variant of ISO 646 [ISO646]. The JIS X 0208 [JISX0208] character sets consist of Kanji, Hiragana, Katakana and some other symbols and characters. Each character takes up two bytes. For further details about the JIS Japanese national character set standards, refer to [JISX0201] and [JISX0208]. For further information about the escape sequences, see [ISO2022] and [ISOREG]. If there are JIS X 0208 characters on a line, there must be a switch to ASCII or to the "Roman" set of JIS X 0201 before the end of the line (i.e. before the CRLF). This means that the next line starts in the character set that was switched to before the end of the previous line. Also, the message body must end with CRLF, and there must be a switch to ASCII before the last CRLF (if there are any non-ASCII characters in the message body). Other restrictions are given in the Formal Syntax below. Murai et al Expires 1st June 1993 [Page 2] Internet Draft Updated 1st December 1992 Formal Syntax The notational conventions used here are identical to those used in RFC 822 [RFC822]. The * (asterisk) convention is as follows: l*m something meaning at least l and at most m somethings, with l and m taking default values of 0 and infinity, respectively. line = *text *1( *segment single-byte-seq *text ) CRLF segment = single-byte-segment / double-byte-segment single-byte-segment = single-byte-seq 1*text double-byte-segment = double-byte-seq 1*( one-of-94 one-of-94 ) single-byte-seq = ESC "(" ( "B" / "J" ) double-byte-seq = ESC "$" ( "@" / "B" ) ; ( Octal, Decimal.) ESC = <ISO 2022 ESC, escape> ; ( 33, 27.) SI = <ISO 2022 SI, shift-in> ; ( 17, 15.) SO = <ISO 2022 SO, shift-out> ; ( 16, 14.) one-of-94 = <any char in 94-char set> ; (41-176, 33.-126.) CHAR = <any ASCII character> ; ( 0-177, 0.-127.) text = <any CHAR, including bare CR & bare LF, but NOT including CRLF, and not including ESC, SI, SO> MIME Considerations The name given to the JUNET character encoding is "ISO-2022-JP". This name is intended to be used in MIME messages as follows: Content-Type: text/plain; charset=iso-2022-jp Murai et al Expires 1st June 1993 [Page 3] Internet Draft Updated 1st December 1992 The ISO-2022-JP encoding is already in 7-bit form, so it is not necessary to use a Content-Transfer-Encoding header. It should be noted that applying the Base64 or Quoted-Printable encoding will render the message unreadable in current JUNET software. Background Information The JUNET encoding was described in the JUNET User's Guide [JUNET] (JUNET Riyou No Tebiki Dai Ippan). The encoding is based on the particular usage of ISO 2022 announced by 4/1 (see [ISO2022] for details). However, the escape sequence normally used for this announcement is not included in ISO-2022-JP messages. The so-called half-width (hankaku) Katakana, that is, the Kana set of JIS X 0201, are not used in ISO-2022-JP messages. In the past, some systems erroneously used the escape sequence ESC ( H in JUNET messages. This escape sequence is officially registered for a Swedish character set [ISOREG], and should not be used in ISO- 2022-JP messages. Some systems do not distinguish between ESC ( B and ESC ( J or between ESC $ @ and ESC $ B for display. However, when relaying a message to another system, the escape sequences must not be altered in any way. 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 JIS X 0208 character takes up two columns, and the escape sequences do not take up any columns. The implementor is reminded that JIS X 0208 characters take up two bytes and should not be split in the middle to break lines for displaying, etc. The JIS X 0208 standard was revised in 1990, to add two characters at the end of the table. Although ISO 2022 specifies special additional escape sequences to indicate the use of revised character sets, it is suggested here not to make use of this special escape sequence in ISO-2022-JP text, even if the two characters added to JIS X 0208 in 1990 are used. Murai et al Expires 1st June 1993 [Page 4] Internet Draft Updated 1st December 1992 References [ASCII] American National Standards Institute, "Coded character set -- 7-bit American national standard code for information interchange", ANSI X3.4-1968 [ISO646] International Organization for Standardization (ISO), "Information processing -- ISO 7-bit coded character set for information interchange", International Standard, Ref. No. ISO 646- 1983 (E) [ISO2022] 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) [ISOREG] International Organization for Standardization (ISO), "International Register of Coded Character Sets To Be Used With Escape Sequences" [JISX0201] Japanese Standards Association, "Code for Information Interchange", JIS X 0201-1976 [JISX0208] Japanese Standards Association, "Code of the Japanese graphic character set for information interchange", JIS X 0208-1978, -1983 and -1990 [JUNET] JUNET Riyou No Tebiki Sakusei Iin Kai (JUNET User's Guide Drafting Committee), "JUNET Riyou No Tebiki (Dai Ippan)" ("JUNET User's Guide (First Edition)"), February 1988 [MIME] Nathaniel Borenstein and Ned Freed, "MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies", Proposed (Internet) standard, June 1992, rfc1341 [RFC822] David H. Crocker, "Standard for the Format of ARPA Internet Text Messages", Internet standard, August 1982, rfc822 [RFC1036] M. Horton and R. Adams, "Standard for Interchange of USENET Messages", December 1987, rfc1036 [RFC1342] Keith Moore, "Representation of Non-ASCII Text in Internet Message Headers", Proposed (Internet) standard, June 1992, rfc1342 Security Considerations Murai et al Expires 1st June 1993 [Page 5] Internet Draft Updated 1st December 1992 Security considerations are not discussed in this memo. Acknowledgements Many people assisted in drafting this document. The authors wish to thank in particular Akira Kato, Masahiro Sekiguchi and Ken'ichi Handa. Authors' Addresses Jun Murai Keio University 5322 Endo, Fujisawa Kanagawa 252 Japan Fax: +81 (466) 49-1101 EMail: firstname.lastname@example.org Mark Crispin Panda Programming 6158 Lariat Loop NE Bainbridge Island, WA 98110-2098 USA Phone: +1 (206) 842-2385 EMail: MRC@PANDA.COM Erik M. van der Poel A-105 Park Avenue 4-4-10 Ohta, Kisarazu Chiba 292 Japan Phone: +81 (438) 22-5836 Fax: +81 (438) 22-5837 EMail: email@example.com Murai et al Expires 1st June 1993 [Page 6]