The named item is sought first in
metadata, where an exact match to the name is required. If
it is not present in the metadata slot, then a partial-name
match is sought in the data slot. Failing both
tests, an exact-name match is sought in a field named
dataNamesOriginal in the object's metadata
slot, if that field exists. Failing that, NULL is returned.
To get information on the specialized variants of this function,
type e.g. ?"[[,adv-method" for information on extracting
data from an object of adv-class.