For information on converting to InterSystems IRIS,
see the InterSystems IRIS Adoption Guide
and the InterSystems IRIS In-Place Conversion Guide,
both available on the WRC Distributions page (login required).
Inherited description: Used for enumerated (multiple-choice) attributes.
VALUELIST is either a null string ("") or a delimiter
separated list (where the delimiter is the first character) of logical values.
If a non-null value is present, then the attribute is restricted to values
in the list, and the validation code simply checks to see if the value is in the list.