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

[Drew Adams]

> > > [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.
> 
> Isn't it clear already?

I meant [:xdigit:], not [:digit:], in my reply.  Sorry for
the typo.