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 Tamaru Informational
