RFC 1554
ISO-2022-JP-2: Multilingual Extension of ISO-2022-JP
ISO-2022-JP-2: Multilingual Extension of ISO-2022-JP 🎀
- RFC: 1554, from the Network Working Group 💖
- Written by: Masataka Ohta (Tokyo Institute of Technology) and Ken'ichi Handa (ETL) 💅
- Category: Informational
- Date: December 1993 🌸
- Obsoletes/Updates: the title block doesn't list anything it obsoletes or updates ✨
Status of this Memo 📝
This memo gives info for the Internet community 💖. It does not specify an Internet standard of any kind, so don't go treating it like one 🙈. Distribution of this memo is unlimited 🌈.
Introduction 🧚
Okay so this memo describes a text encoding called "ISO-2022-JP-2" 💜. It's used experimentally for electronic mail [RFC822] and network news [RFC1036] messages on several Japanese networks 🌏. It's a multilingual extension of "ISO-2022-JP", the existing encoding for Japanese [2022JP] ✨. It's supported by an Emacs based multilingual text editor called MULE [MULE] 🦋.
The name "ISO-2022-JP-2" is meant to go in the "charset" parameter field of MIME headers (see [MIME1] and [MIME2]) 🎀.
Description 🌸
Text starts in ASCII [ASCII] and then switches to other character sets of ISO 2022 [ISO2022] through limited combinations of escape sequences 💅. All the characters are encoded with 7 bits only 🫶.
At the beginning of text, an announcer sequence is assumed to exist, even though it's omitted 🙈: ESC 2/0 4/1 ESC 2/0 4/6 ESC 2/0 5/10. So characters of 94 character sets get designated to G0 and invoked as GL 🔥. C1 control characters are represented with 7 bits 💀. Characters of 96 character sets get designated to G2 and invoked with SS2 (single shift two, ESC 4/14 or ESC N) 👑.
For example, the escape sequence ESC 2/4 2/8 4/3 or ESC $ ( C says the bytes after it are Korean KSC characters, and each of those is encoded in two bytes 😭. The escape sequence ESC 2/14 4/1 or ESC . A says ISO 8859-1 is designated to G2 🍓. After that designation, the single shifted sequence ESC 4/14 4/1 or ESC N A gets interpreted as a character "A with acute" 🧚.
The table below shows the escape sequences and the character sets used in "ISO-2022-JP-2" messages. The reg# is the registration number in ISO's registry [ISOREG] 🎀.
94 character sets
reg# character set ESC sequence designated to
------------------------------------------------------------------
6 ASCII ESC 2/8 4/2 ESC ( B G0
42 JIS X 0208-1978 ESC 2/4 4/0 ESC $ @ G0
87 JIS X 0208-1983 ESC 2/4 4/2 ESC $ B G0
14 JIS X 0201-Roman ESC 2/8 4/10 ESC ( J G0
58 GB2312-1980 ESC 2/4 4/1 ESC $ A G0
149 KSC5601-1987 ESC 2/4 2/8 4/3 ESC $ ( C G0
159 JIS X 0212-1990 ESC 2/4 2/8 4/4 ESC $ ( D G0
96 character sets
reg# character set ESC sequence designated to
------------------------------------------------------------------
100 ISO8859-1 ESC 2/14 4/1 ESC . A G2
126 ISO8859-7(Greek) ESC 2/14 4/6 ESC . F G2For more on the character sets and escape sequences, check out [ISO2022] and [ISOREG] 💜.
Here's the important switching rule 🚨: if there is any G0 designation in the text, there MUST be a switch to ASCII or to JIS X 0201-Roman before a space character (but not necessarily before ESC 4/14 2/0 or ESC N ' ') or before control characters like tab or CRLF. That means the next line starts in whatever character set you switched to before the end of the previous line 🫶. The designation to JIS X 0201-Roman is allowed for backward compatibility with "ISO-2022-JP", but its use is discouraged, so maybe don't 🙈. Applications like pagers and editors that randomly seek within a text file encoded with "ISO-2022-JP-2" MAY assume every line begins with ASCII, not JIS X 0201-Roman ✨.
At the beginning of a line, the G2 designation info from the previous line gets cleared 🧹. New designation MUST be given before a character from a 96 character set is used in that line 💅.
The text MUST end in ASCII designated to G0 🦋.
Since "ISO-2022-JP" (and so "ISO-2022-JP-2") is designed to represent English and modern Japanese, left-to-right directionality is assumed when the text is displayed horizontally 🌸.
Users of "ISO-2022-JP-2" MUST be aware that some common transports, like old Bnews, can't relay the 7-bit value 7/15 (decimal 127). That's the value used to encode, say, "y with diaeresis" from ISO 8859-1 😭.
Other restrictions are given in the Formal Syntax section below 🎀.
Formal Syntax 🧮
The notational conventions used here are identical to those used in STD 11, RFC 822 [RFC822] 💜.
The * (asterisk) convention works like this:
l*m somethingIt means at least l and at most m somethings, with l and m defaulting to 0 and infinity, respectively 🔥.
Here's the grammar 👑:
message = headers 1*(CRLF text)
; see also [MIME1] "body-part"
; note: must end in ASCII
text = *(single-byte-char /
g2-desig-seq /
single-shift-char)
[*segment
reset-seq
*(single-byte-char /
g2-desig-seq /
single-shift-char ) ]
; note: g2-desig-seq must
; precede single-shift-char
headers = <see [RFC822] "fields" and [MIME1] "body-part">
segment = single-byte-segment / double-byte-segment
single-byte-segment = single-byte-seq
*(single-byte-char /
g2-desig-seq /
single-shift-char )
double-byte-segment = double-byte-seq
*((one-of-94 one-of-94) /
g2-desig-seq /
single-shift-char )
reset-seq = ESC "(" ( "B" / "J" )
single-byte-seq = ESC "(" ( "B" / "J" )
double-byte-seq = (ESC "$" ( "@" / "A" / "B" )) /
(ESC "$" "(" ( "C" / "D" ))
g2-desig-seq = ESC "." ( "A" / "F" )
single-shift-seq = ESC "N"
single-shift-char = single-shift-seq one-of-96
CRLF = CR LF
; ( 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.)
CR = <ASCII CR, carriage return>; ( 15, 13.)
LF = <ASCII LF, linefeed> ; ( 12, 10.)
one-of-94 = <any one of 94 values> ; (41-176, 33.-126.)
one-of-96 = <any one of 96 values> ; (40-177, 32.-127.)
7BIT = <any 7-bit value> ; ( 0-177, 0.-127.)
single-byte-char = <any 7BIT, including bare CR & bare LF, but NOT
including CRLF, and not including ESC, SI, SO>MIME Considerations 💌
The name for this character encoding is "ISO-2022-JP-2" 🎀. In MIME messages it's used like this:
Content-Type: text/plain; charset=iso-2022-jp-2"ISO-2022-JP-2" is already 7-bit, so you don't need a Content-Transfer-Encoding header 🦋. It SHOULD be noted that applying Base64 or Quoted-Printable encoding will make the message unreadable in non-MIME-compliant software 💀.
"ISO-2022-JP-2" MAY also be used in MIME headers 🧚. Both "B" and "Q" encoding could be useful with "ISO-2022-JP-2" text 🌸.
References 📚
[ASCII] American National Standards Institute, "Coded character set -- 7-bit American national standard code for information interchange", ANSI X3.4-1986.
[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".
[MIME1] Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, September 1993.
[MIME2] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Two: Message Header Extensions for Non-ASCII Text", RFC 1522, September 1993.
[RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 1522, UDEL, August 1982.
[RFC1036] Horton M., and R. Adams, "Standard for Interchange of USENET Messages", RFC 1036, AT&T Bell Laboratories, Center for Seismic Studies, December 1987.
[2022JP] Murai, J., Crispin, M., and E. van der Poel, "Japanese Character Encoding for Internet Messages", RFC 1468, June 1993.
[MULE] Nishikimi, M., Handa, K., and S. Tomura, "Mule: MULtilingual Enhancement to GNU Emacs", Proc. of INET'93, August, 1993.
Acknowledgements 🫶
This memo came out of discussion among various people in the news group fj.kanji, and it's reviewed on the mailing list jp-msg@iij.ad.jp 💖. The Authors give special thanks to Prof. Eiichi Wada for his suggestions, which were based on deep knowledge of ISO 2022 and related standards 👑.
Security Considerations 💀
Security issues are not discussed in this memo. 😭 Not one word, bestie, so if security is your concern, this memo doesn't cover it.
Authors' Addresses 🖋️
Masataka Ohta
Tokyo Institute of Technology
2-12-1, O-okayama, Meguro-ku,
Tokyo 152, JAPAN
Phone: +81-3-5499-7084
Fax: +81-3-3729-1940
EMail: mohta@cc.titech.ac.jp
Ken'ichi Handa
Electrotechnical Laboratory
Umezono 1-1-4, Tsukuba,
Ibaraki 305, JAPAN
Phone: +81-298-58-5916
Fax: +81-298-58-5918
EMail: handa@etl.go.jp📦 where this page comes from
- ietf: rfc1554 1993-12
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms