Peter,
> I consider contrib/isn to be quite broken. It hard codes ISBN
> prefixes
> for the purposes of sanitising ISBNs, even though their assignment is
> actually controlled by a decentralised body of regional authorities.
> I'd vote for kicking it out of contrib.
Submit a patch to fix it then.
I use ISBN in 2 projects, and it's working fine for me. I'll strongly resist any attempt to "kick it out".
--Josh Berkus