ONAREA returns a character string whose value is the name of the
AREA reference for which an AREA condition is raised. If the reference
includes DBCS names, the string returned is a mixed character string.
It is in context in an ON-unit (or any of its dynamic descendants)
for the AREA condition, or for the ERROR or FINISH condition raised
as the implicit action for an AREA condition.
>>-ONAREA-+----+----------------------------------------------->< '-()-'
If the ONAREA built-in function is used out of context, a null string is returned.
If the AREA reference is excessively long or complicated, a null string is returned.