Re: "Coding system"? Eh?

[Lars Magne Ingebrigtsen <larsi@gnus.org>]

davidk@lysator.liu.se (David Kågedal) writes:

> ISO 8859-1 is both a character set, and an encoding (one-to-one from
> charater to byte), I believe.  But I'm not sure how it is defined.

A character set is an encoding in normal usage.  Quoth RFC2045:

2.2.  Character Set

   The term "character set" is used in MIME to refer to a method of
   converting a sequence of octets into a sequence of characters.  Note
   that unconditional and unambiguous conversion in the other direction
   is not required, in that not all characters may be representable by a
   given character set and a character set may provide more than one
   sequence of octets to represent a particular sequence of characters.

   This definition is intended to allow various kinds of character
   encodings, from simple single-table mappings such as US-ASCII to
   complex table switching methods such as those that use ISO 2022's
   techniques, to be used as character sets.  However, the definition
   associated with a MIME character set name must fully specify the
   mapping to be performed.  In particular, use of external profiling
   information to determine the exact mapping is not permitted.

   NOTE: The term "character set" was originally to describe such
   straightforward schemes as US-ASCII and ISO-8859-1 which have a
   simple one-to-one mapping from single octets to single characters.
   Multi-octet coded character sets and switching techniques make the
   situation more complex. For example, some communities use the term
   "character encoding" for what MIME calls a "character set", while
   using the phrase "coded character set" to denote an abstract mapping
   from integers (not octets) to characters.

-- 
(domestic pets only, the antidote for overdose, milk.)
  larsi@gnus.org * Lars Magne Ingebrigtsen