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

[Drew Adams <drew.adams@oracle.com>]

> > In the context of bug 47455 the idea emerged that it can be useful
> > to have a minor mode that highlights non-ascii characters.  I want
> > to ask hear for feedback: does such a mode already exist?  Can it be
> > useful to have this minor mode more general such that the highlighted
> > character classes become configurable?  Are there possible use cases
> > for this beyond non-ascii characters?

Eli> We already highlight some potentially confusing characters,
Eli> see no-break-char-display and faces nobreak-space and
Eli> nobreak-hyphen.

OF> Highlighting characters that does not belong to certain
OF> coding system would be useful to me.
OF>
OF> Sometimes I work on source code encoded as UTF-8 but they
OF> must not contain characters not encodable by windows-1252.
OF> More precisely, string literals must be composed of
OF> characters encodable by windows-1252.

That highlighting of no-break chars is limited.

1. You can't specify which no-break chars you want to highlight,
   and you can't highlight different such chars differently.

2. It is low-level highlighting, which doesn't use font-lock.

`whitespace.el' is similarly limited, e.g. coupling space and
hard-space chars, for highlighting.

More useful is something like what library `highlight-chars.el'
offers.  You can highlight any chars you like, in any way you
like.  You can highlight arbitrary chars, chars in char ranges,
char classes, or charsets.

https://www.emacswiki.org/emacs/ShowWhiteSpace#HighlightChars

https://www.emacswiki.org/emacs/download/highlight-chars.el