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

[Eli Zaretskii]

> Date: Tue, 11 Jun 2019 10:19:17 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: mattiase@acm.org, eggert@cs.ucla.edu, 36167@debbugs.gnu.org,
>         hi-angel@yandex.ru
> 
> > Isn't it clear already?
> 
> I meant [:xdigit:], not [:digit:], in my reply.  Sorry for
> the typo.

:xdigit: is also clearly documented:

  ‘[:xdigit:]’
       This matches the hexadecimal digits: ‘0’ through ‘9’, ‘a’ through
       ‘f’ and ‘A’ through ‘F’.