bug#1723: 23.0.60; Odd behaviour with #'check-coding-systems-region

[Chong Yidong]

It appears that check-coding-systems-region can return t under some
circumstances, but this is not documented in the docstring, nor in the
elisp manual.  Could you update the documentation?  Or, you can explain
the circumstances under which this happens so that someone else can do
the updating.

Thanks.

Aidan Kehoe <kehoea@parhasard.net> wrote:

> The check-coding-systems-region docstring says this: 
>
>   (check-coding-systems-region start end coding-system-list)
>  
>   Check if the region is encodable by coding systems.
>  
>   The value is an alist ((CODING-SYSTEM POS0 POS1 ...) ...), where
>   CODING-SYSTEM is a member of coding-system-list and can't encode the
>   whole region, POS0, POS1, ... are buffer positions where non-encodable
>   characters are found.
>  
>   If all coding systems in coding-system-list can encode the region, the
>   value is nil.
>   [...]
>
> It is unclear to me what "value" means there. My provisional
> assumption was that it meant "return value", but that doesn't reflect
> the behaviour of the function:

>   (with-temp-buffer (insert "a") (check-coding-systems-region
>   (point-min) (point-max) '(iso-8859-1)))
>   => t