Re: coding systems and input methods are non-intuitive stuff

[David Kastrup]

Kevin Rodgers <address@hidden> writes:

> Juanma Barranquero wrote:
>> C-x b *scratch* RET
>> C-x RET f latin-1 RET          ; buffer coding system = latin-1
>> C-u C-\ romanian-prefix RET    ; input method: romanian-prefix
>> ,s                             ; character: ş (2362, #o4472, #x93a,
>>                               ;   U+015F)
>> <left> M-x quail-show-key RET  ; To input `ş', type ",s"
>> <right>
>> C-x RET f utf-8 RET            ; buffer coding system = utf-8
>>                               ; input method: the same as before
>> ,s                             ; character: ş (331903, #o1210177,
>>                               ;   #x5107f, U+015F)
>> <left> M-x quail-show-key RET  ; ş can't be input by the current
>>                               ;   input method
>>
>> Now, I understand that the buffer code for these characters is not the
>> same... but it is quite weird nonetheless to input a character with
>> the current input method, and afterwards be told that it "can't be
>> input by the current input method".
>
> The thing that confuses me is that the ISO 8859-1 character set (which
> is what the latin-1 coding system encodes, right?) only contains U+0000
> - U+00FF.  So how does U+015F get inserted into a latin-1 buffer?

There is no such thing as a "latin-1 buffer" in Emacs.  Buffers are
always encoded in emacs-mule (well, we still have something called
"unibyte" buffers, but they are really only for binary data).  The
buffer contains characters.  Code points of a particular coding system
are only associated when saving, loading, communicating with
processes, X selections, networks, keyboards, terminals.  All those
operations have their own coding systems.  The buffer itself hasn't.

-- 
David Kastrup