Re: Emacs 23 character code space

[Eli Zaretskii <eliz@gnu.org>]

> From: Kenichi Handa <handa@m17n.org>
> CC: eliz@gnu.org, emacs-devel@gnu.org
> Date: Wed, 26 Nov 2008 13:58:26 +0900
> 
> I'll explain it a little bit more.  To decode a character
> sequence to a byte sequence, Emacs actually does two kinds
> of decoding as below:
> 
>              (1)                                (2)
> characters <-----> (charset code-point) pairs <-----> bytes

Can you give a couple of examples, for some popular charsets, and how
we decode bytes into characters thru these pairs of charsets and code
points?

> For the decoding of (1), Emacs uses infomaiton of coding
> system to decide which charset to use, and then uses
> informaiton of the selected charset to get a code point.
> 
> For the decoding of (2) Emacs uses only information of
> coding system.

Thanks.  What confuses me is that, roughly, there's a charset in Emacs
23 for every coding-system, and they both have almost identical names.
For example, the code point of a-umlaut in the iso-8859-1 charset is
exactly identical to the byte value produced by encoding that
character with iso-8859-1 coding-system.  So I wonder why we need
both in Emacs.  Why can't we, for example, decode bytes directly into
Emacs characters?