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INFORMATIONAL

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".



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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.



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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" )) /



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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.






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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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