[Koha] Authorized values

[Bob Ewart]

We need a way to link family members together.

I can setup an additional attribute, Family, which could be repeated.  
The value would be the card  number of one of the other members of the 
family.

Ideally it would be a valid card number, however limiting it to 4 or 5 
digits would at least give a sanity check.

Authorized values are fixed constants.  Having a way to specify a 
pattern would be very useful.

-- 
Bob Ewart