ISO-2022-JP-2: Multilingual Extension of ISO-2022-JP
RFC 1554

Document Type RFC - Informational (December 1993; No errata)
Last updated 2013-03-02
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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]
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