|in addition to storing info
about a physical item, a MARC record can either link that same description
for a digital copy of it (see the records in the catalog for anything in
VARIATIONS), or they could describe only a digital item. There's a standing
debate out there about how to deal with an item held both analog and digital,
whether to have one record describing the physical item but having a URL for
the digitized version, or having two separate records.