Network Working Group K. Tamaru
Request for Comments: 2237 Microsoft Corporation
Category: Informational November 1997
Japanese Character Encoding for Internet Messages
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (1997). All Rights Reserved.
This memo defines an encoding scheme for the Japanese Characters,
describes "ISO-2022-JP-1", which is used in electronic mail [RFC-
822], and network news [RFC 1036]. Also this memo provides a listing
of the Japanese Character Set that can be used in this encoding
2. Requirements Notation
This document uses terms that appear in capital letters to indicate
particular requirements of this specification. Those terms are
"MUST", "SHOULD", "MUST NOT", "SHOULD NOT", and "MAY". The meaning of
each term are found in [RFC-2119]
RFC 1468 defines the way Japanese Characters are encoded, likewise
what this memo defines. It defines the use of JIS X 0208 as the
double-byte character set in ISO-2022-JP text.
Today, many operating systems support proprietary extended Japanese
characters or JIS X 0212, This includes the Unicode character set,
which does not conform to JIS X 0201 nor JIS X 0208. Therefore, this
limits the ability to communicate and correspond precise information
because of the limited availability of Kanji characters. Fortunately
JIS (Japanese Industry Standard) defines JIS X 0212 as "code of the
Tamaru Informational [Page 1]RFC 2237 Japanese Character Encoding November 1997
supplementary Japanese graphic character set for information
interchange". Most Japanese characters which are used in regular
electronic mail in most cases can be accommodated in JIS X 0201, JIS
X 0208 and JIS X 0212.
Also it is recognized that there is a tendency to use Unicode,
however, Unicode is not yet widely used and there is a certain
limitation with old electronic mail system. Furthermore, the purpose
of this comment is to add the capability of writing out JIS X 0212.
This comment does not describe any representation of iso-2022-jp-1
version information in addition to JIS X 0212 support.
In "ISO-2022-JP-1" text, the initial character code of the message is
in ASCII. The "double-byte-seq"(see "Format Syntax" section) (ESC "$"
"B" / ESC "$" "@" / ESC "$" "(" "D") is the only designator that
indicates that the following character is double-byte, and it is
valid until another escape sequence appears. It is very discouraged
to use (ESC "$" "@") for double byte character encoding, new
implementation SHOULD use only (ESC "$" "B") for double byte encoding
The end of "ISO-2022-JP-1" text MUST be in ASCII. Also it is strongly
recommended to back up to the ASCII at the end of each line rather
than JIS X 0201-Roman if there is any none ASCII character in middle
of a line.
Since "ISO-2022-JP-1" is designed to add the capability of writing
out JIS X 0212, if the message does not contain none of JIS X 0212
characters. "ISO-2022-JP" text MUST BE used.
JIS X 0201-Roman is not identical to the ASCII with two different
The following list are the escape sequences and character sets that
can be used in "ISO-2022-JP-1" text. The registered number in the ISO
2375 Register which allow double-byte ideographic scripts to be
encoded within ISO/IEC 2022 code structure is indicated as reg#
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
159 JIS X 0212-1990 ESC 2/4 2/8 4/4 ESC $ ( D G0
Tamaru Informational [Page 2]RFC 2237 Japanese Character Encoding November 1997
Other restrictions are given in the Formal Syntax below.
5. Formal Syntax