RFC 2237 (rfc2237) - Page 2 of 6
Japanese Character Encoding for Internet Messages
Alternative Format: Original Text Document
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.
4. Description
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
instead.
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
characters.
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#
below.
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
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