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rfc:rfc1554

Network Working Group M. Ohta Request for Comments: 1554 Tokyo Institute of Technology Category: Informational K. Handa

                                                                   ETL
                                                         December 1993
        ISO-2022-JP-2: Multilingual Extension of ISO-2022-JP

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.

Introduction

 This memo describes a text encoding scheme: "ISO-2022-JP-2", which is
 used experimentally for electronic mail [RFC822] and network news
 [RFC1036] messages in several Japanese networks.  The encoding is a
 multilingual extension of "ISO-2022-JP", the existing encoding for
 Japanese [2022JP].  The encoding is supported by an Emacs based
 multilingual text editor: MULE [MULE].
 The name, "ISO-2022-JP-2", is intended to be used in the "charset"
 parameter field of MIME headers (see [MIME1] and [MIME2]).

Description

 The text with "ISO-2022-JP-2" starts in ASCII [ASCII], and 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, the existence of an announcer sequence:
 "ESC 2/0 4/1 ESC 2/0 4/6 ESC 2/0 5/10" is (though omitted) assumed.
 Thus, characters of 94 character sets are designated to G0 and
 invoked as GL.  C1 control characters are represented with 7 bits.
 Characters of 96 character sets are 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"
 indicates that the bytes following the escape sequence are Korean KSC
 characters, which are encoded in two bytes each.  The escape sequence
 "ESC 2/14 4/1" or "ESC . A" indicates that ISO 8859-1 is designated
 to G2. After the designation, the single shifted sequence "ESC 4/14
 4/1" or "ESC N A" is interpreted to represent a character "A with
 acute".

Ohta & Handa [Page 1] RFC 1554 Multilingual Extension of ISO-2022-JP December 1993

 The following table gives 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    G2
 For further information about the character sets and the escape
 sequences, see [ISO2022] and [ISOREG].
 If there is any G0 designation in 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 control
 characters such as tab or CRLF.  This means that the next line starts
 in the character set that was switched to before the end of the
 previous line.  Though the designation to JIS X 0201-Roman is allowed
 for backward compatibility to "ISO-2022-JP", its use is discouraged.
 Applications such as pagers and editors which randomly seek within a
 text file encoded with "ISO-2022-JP-2" may assume that all the lines
 begin with ASCII, not with JIS X 0201-Roman.
 At the beginning of a line, information on G2 designation of the
 previous line is cleared.  New designation must be given before a
 character in 96 character sets is used in the line.
 The text must end in ASCII designated to G0.
 As the "ISO-2022-JP", and thus, "ISO-2022-JP-2", is designed to
 represent English and modern Japanese, left-to-right directionality
 is assumed if the text is displayed horizontally.
 Users of "ISO-2022-JP-2" must be aware that some common transport
 such as old Bnews can not relay a 7-bit value 7/15 (decimal 127),
 which is used to encode, say, "y with diaeresis" of ISO 8859-1.

Ohta & Handa [Page 2] RFC 1554 Multilingual Extension of ISO-2022-JP December 1993

 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 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.
 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" )) /

Ohta & Handa [Page 3] RFC 1554 Multilingual Extension of ISO-2022-JP December 1993

                       (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 given to the character encoding is "ISO-2022-JP-2". This
 name is intended to be used in MIME messages as follows:
    Content-Type: text/plain; charset=iso-2022-jp-2
 The "ISO-2022-JP-2" 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 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.

Ohta & Handa [Page 4] RFC 1554 Multilingual Extension of ISO-2022-JP December 1993

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 is the result of discussion between various people in a
 news group: fj.kanji and is reviewed by a mailing list: jp-msg
 @iij.ad.jp.  The Authors wish to thank in particular Prof. Eiichi
 Wada for his suggestions based on profound knowledge in ISO 2022 and
 related standards.

Ohta & Handa [Page 5] RFC 1554 Multilingual Extension of ISO-2022-JP December 1993

Security Considerations

 Security issues are not discussed in this memo.

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

Ohta & Handa [Page 6]

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