RFC 1502 (rfc1502) - Page 2 of 14

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RFC 1502          X.400 Use of Extended Character Sets       August 1993


   The author believes that this document gives a specification that can
   easily accomodate the use of any character set in the ISO registry,
   and, by giving guidance rules for choosing character sets, will help
   interworking.

2.2.  Families of character sets

2.2.1.  ISO 6937/T.61

   ISO 6937 is a code technique used and recommended in T.51 and T.101
   (Teletex and Videotex service) and in X.500, providing a repertoire
   of 333 characters from the Latin script by use of non- spacing
   diacritical marks. It corresponds closely to CCITT recommendation
   T.61.

   The problem with that technique is that the character stream comes in
   two modes, i.e., some characters are coded with one byte and some
   with two (composite characters). This makes information processing
   systems such as an E-mail UA or GW more complex.

   It is also not extensible to other languages like Korean or Chinese,
   or even Greek, without invoking the character set switching
   techniques of ISO 2022.

2.2.2.  ISO 8859

   ISO 8859 defines a set of character sets, each suitable for use in
   some group of languages. Each character in ISO 8859 is coded in a
   single byte.

   There are currently 11 parts of ISO 8859, plus a "supplementary" set,
   registered as ISO IR 154. Most languages using single-byte characters
   can be written in one or another of the ISO 8859 sets.  There are
   sets covering Greek, Hebrew and Arabic, but there is still
   controversy over the problem of the rendering direction for Hebrew
   and Arabic.

   All the ISO 8859 sets include US-ASCII as a subset. All use 8 bits.

   ISO 8859 is regarded by many as a solution; for instance, the X
   windows system now comes with ISO-8859-1 as the "standard" character
   set, with the possibility of specifying others. But since the same
   applications often do not support character set switching within
   text, it is problematic to use these in a truly multilingual
   environment.  (Also, most fonts claiming to be "ISO- 8859-1" in X11R5
   are actually 7-bit fonts. The implied lie is very unfortunate.)





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