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Network Working Group                                            M. OhtaRequest For Comments: 1815                 Tokyo Institute of TechnologyCategory: Informational                                        July 1995Character Sets ISO-10646 and ISO-10646-J-1Status 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.Abstract   Though the ISO character set standard of ISO 10646 is specified   reasonably well about European characters, it is not so useful in an   fully internationalized environment.   For the practical use of ISO 10646, a lot of external profiling such   as restriction of characters, restriction of combination of   characters and addition of language information is necessary.   This memo provides information on such profiling, along with charset   names to each profiled instance.   Though all the effort is done to make the resulting charset as useful   10646 based charset as possible, the result is not so good.  So, the   charsets defined in this memo are only for reference purpose and its   use for practical purpose is strongly discouraged.Introduction   This memo describes two text encoding schemes based on ISO 10646   [10646].   As ISO 10646 specifies too little about how text is visualized, to   practically use ISO 10646, it is necessary to restrict the standard   minimally and then add some amount of profiling information.   For ISO 2022 [ISO2022] based national standards, sufficient profiling   information is provided by national standardization bodies, but, for   ISO 10646, such a profiling is not yet provided.   As the profiling of ISO 10646 largely affects which character or   combination of characters could be properly displayed, changes of   profiling of ISO 10646 are as significant as additions of new   character sets of ISO 2022.M. Ohta                      Informational                      [Page 1]

RFC 1815       Character Sets ISO-10646 and ISO-10646-J-1      July 1995   That is, it's impractical to support the entirety of ISO 10646 (new   restriction or profiling can always be added), so a client needs to   know whether some restriction or profiling is being used before it   can decide whether to display the body part. Thus, it is necessary to   provide multiple charset names to each variation of ISO 10646.   For example, in Japan with Japanese windows NT, only those Han   characters already supported by MS Kanji code (mostly equivalent to   JIS X 0208 [JISX0208]) can be displayed, because no other font   pattern is commonly provided.   The other problem of ISO 10646 for Han characters is that, to display   them in quality required for daily plain text processing in   China/Japan/Korea, it is necessary to add profiling information on   which one of Chinese/Japanese/Korean the text is using.  It should be   noted that this feature makes multilingual mixed   Chinese/Japanese/Korean text with ISO 10646 impractical.   Also, just as [RFC1521] was unclear about how bi-directionality   should be supported with "ISO-8859-6" and "ISO-8859-8" which was   corrected by [RFC1556], it is also unclear how bi-directionality   could be supported with ISO 10646.  There are too much ways to   support bi- directionality.  So, until some bi-directionality   mechanism(s) becomes widely supported, it is necessary to exclude   characters for languages which requires bi-directionality support   from the minimal variation.  It should be noted that, though ISO   10646 is intended to be free from long term states, save for some   profiling information, introduction of bi-directionality with ISO   10646 do requires the long term states.   Combining characters also cause problems. In many countries where   combining characters based on [ISO2022] is used, there are   restrictions on how combining characters are ordered [TIS].  Without   such restriction, the result of combination is completely meaningless   which is the current state of ISO 10646.  That is, if some   combination is allowed in some implementation while the other does   not support it, communication between them is difficult unless ISO   10646 is profiled to be least common set of widely supported   combinations.  So, again, until combination restriction will be   developed for each language, it is necessary to exclude characters   for such languages from the minimal variation.   Conjoining characters also, may or may not be supported, which   requires another profiling.   According to those considerations, this memo defines two variations   of ISO 10646. They are "ISO-10646" as the minimal basic variation and   "ISO-10646-J-1" as the variation which could be useful in Japan.M. Ohta                      Informational                      [Page 2]

RFC 1815       Character Sets ISO-10646 and ISO-10646-J-1      July 1995   Finally, this memo, by no means, promotes the use of ISO 10646 on the   Internet.  It's use is strongly discouraged, when there are other   charsets which can encode the same information, Families of ISO 10646   based charsets, like ISO 2022 based charsets, only forms set of   mutually incompatible encoding systems and, unlike ISO 2022 based   charsets [2022INT], they can not be merged together to be the single   world wide charset.Description of "ISO-10646"   ISO-10646 is profiled to be the most basic part of the family of   encodings based on ISO 10646 and contains the following minimal   graphic characters:      collection number and name      positions      further restriction      ------------------------------------------------------------------      1 BASIC LATIN                   0020-007E      2 LATIN-1 SUPPLEMENT            00A0-00FF   C0 and C1 control characters may also be used as specified in thesection 16 of ISO 10646.   The text with "ISO-10646" encodes text in 16 bit big endian form.   As no combining characters are included, "ISO-10646" can be used with   applications at implementation level 1.   Left-to-right directionality should be used.   The encoding is implemented by Windows/NT.   For practical communication, use of "ISO-10646" is discouraged.   "ISO-8859-1" [RFC1345] should be used instead.M. Ohta                      Informational                      [Page 3]

RFC 1815       Character Sets ISO-10646 and ISO-10646-J-1      July 1995Description of "ISO-10646-J-1"   ISO-10646-J-1 is profiled to be useful for Japanese PC users who use   Japanese version of Windows/NT and contains the following graphic   characters:      collection number and name         positions  further restrictions      ------------------------------------------------------------------      1 BASIC LATIN                      0020-007E      2 LATIN-1 SUPPLEMENT               00A0-00FF      8 BASIC GREEK                      0370-03CF      10 CYRILLIC                        0400-04FF      32 GENERAL PUNCTUATION             2000-206F  See note 1, below.      39 MATHEMATICAL OPERATORS          2200-22FF  See note 1, below.      44 BOX DRAWING                     2500-257F      49 CJK SYMBOLS AND PUNCTUATION     3000-303F  See note 1, below.      50 HIRAGANA                        3040-309F      51 KATAKANA                        30A0-30FF      60 CJK UNIFIED IDEOGRAPHS          4E00-9FFF  See note 1, below.      62 CJK COMPATIBILITY IDEOGRAPHS    F900-FAFF  See note 1, below.      66 CJK COMPATIBILITY FORMS         FE30-FE4F      69 HALFWIDTH AND FULLWIDTH FORMS   FF00-FFEF   Note 1: Most of the characters are excluded.  That is, only those   characters of JIS X 0208 [JISX0208] are included. The reason is that   the Japanese version of Windows/NT have fonts for them only and most   of the users can not read messages which contains other characters.   C0 and C1 control characters may also be used as specified in thesection 16 of ISO 10646.   The text with "ISO-10646-J-1" encodes text in 16 bit big endian form.   Shapes of Han characters should be of Japanese Han, that is, those of   column "J" insection 26 of ISO 10646.   As no combining characters are included, "ISO-10646-J-1" can be used   with applications at implementation level 1.   Characters in "HALFWIDTH AND FULLWIDTH FORMS" compared to be   different characters to the normal width characters.   When text is displayed horizontally, left-to-right directionality   should be used.   For practical communication, use of "ISO-10646-J-1" is discouraged.   ISO-2022-JP" [2022JP] should be used instead.M. Ohta                      Informational                      [Page 4]

RFC 1815       Character Sets ISO-10646 and ISO-10646-J-1      July 1995MIME Considerations   The names given to the character encoding methods described in this   memo are, respectively, "ISO-10646" and "ISO-10646-J-1".  This name   is intended to be used in MIME messages as follows:                Content-Type: text/plain; charset=iso-10646   The ISO-10646 and ISO-10646-J-1 encoding are in 16-bit form, so it is   often necessary to use a Content-Transfer-Encoding header.  Base64   should be useful.   The ISO-10646 and ISO-10646-J-1 may also be used in MIME Part 2   headers [RFC1522].  The "B" encoding should be used with them.References   [10646]     International Organization for Standardization (ISO),               "Universal Multiple-Octet Coded Character Set (UCS)",               International Standard, Ref. No. ISO/IEC 10646-1:1993               (E).   [2022INT]   (An Internet Draft "draft-ohta-text-encoding-*.txt" may               be available).   [2022JP]    Murai, J., Crispin, M., and E. van der Poel, "Japanese               Character Encoding for Internet Messages",RFC 1468, June               1993.   [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).   [JISX0208]  Japanese Standards Association, "Code of the Japanese               graphic character set for information interchange", JIS X               0208-1990.   [RFC1345]   Simonsen, K., "Character Mnemonics & Character Sets",RFC-1345, Rationel Almen Planlaegning, June 1992.   [RFC1521]   Borenstein, N., and Freed, N., "MIME  (Multipurpose               Internet Mail Extensions) Part One: Mechanisms for               Specifying and Describing the Format of Internet Message               Bodies",RFC 1521, September 1993.M. Ohta                      Informational                      [Page 5]

RFC 1815       Character Sets ISO-10646 and ISO-10646-J-1      July 1995   [RFC1522]   Moore, K., "MIME (Multipurpose Internet Mail Extensions)               Part Two: Message Header Extensions for Non-ASCII Text",RFC 1522, September 1993.   [RFC1556]   Nussbacher, H., "Handling of Bi-directional Texts in               MIME"RFC 1556, Israeli Inter-University Computer Center,               December 1993.   [TIS]       Thai Industrial Standard for Thai Character Code for               Computer, TIS 620-2533:1990.Security Considerations   Security issues are not discussed in this memo.Author's Address   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.jpM. Ohta                      Informational                      [Page 6]