bug#36167: [PATCH] Replace manually crafted hex regexes with [[:xdigit:]]

[Eli Zaretskii]

> From: Eli Zaretskii <eliz@gnu.org>
> Cc: mattiase@acm.org, eggert@cs.ucla.edu, 36167@debbugs.gnu.org,
>  hi-angel@yandex.ru
> 
> I'm not against the replacement, I responded to the request to have a
> clear documentation of these character classes.

Specifically, this:

> > [0-9A-Fa-f] still has one advantage: the reader, and the
> > writer, know exactly which characters are included without looking it up. 
> > For
> > example:
> > 
> > - whether upper case, lower case, or both are accepted
> > - whether non-ascii digits are accepted (included in [:digit:] on many
> > platforms)
> 
> +1.  At least the doc for [:digit:] should say exactly
> what it matches.  Then it'll be clear for readers and
> writers.

The last part says "the doc should say" as if the doc doesn't already
say.