Re: minor mode for highlighting character classes such as non-ascii (bug 47455)

["Roland Winkler" <winkler@gnu.org>]

On Tue Jun 1 2021 Daniel Martín wrote:
> There's already a feature in the display engine that shows certain
> non-ASCII characters with a special face.  For example, U+00A0 (no-break
> space) is shown with the ‘nobreak-space’ face, U+00AD (soft hyphen),
> ‘U+2010’ (hyphen), and ‘U+2011’ (non-breaking hyphen) are shown with the
> ‘nobreak-hyphen’ face.  Perhaps your suggestion could be a
> backwards-compatible extension to this hardcoded display mechanism.
> 
> Another option is to simply instruct users to use Hi Lock mode with
> "[^[:ascii:]]".

Thanks, Hi Lock mode seems to be already a close match.  I'll look
at this more closely.

The bug report is related to the fact that \(Bib\|La\)?TeX chokes on
any non-ascii characters.  Nonetheless, non-ascii characters can end
up in such files for all kinds of reasons.  So the idea is to have
something like a minor mode that highlights any non-ascii characters
so that this effectively warns the user about the presence of such
characters.

Personally, I have been fooled in particular by unicode 'ZERO WIDTH
SPACE' which probably requires special treatment.  Could it also
make sense to give this particular character a (possibly configurable)
treatment by the display engine?  (I know nothing about the display
engine.)