DisplayGroup provides an abstraction of a user interface,
comprising of an ordered collection of data objects, some
of which are displayed, and of those some are selected.
Called by the specified object store to determine whether
fetching should continue, where count is the current count
and limit is the limit as specified by the fetch specification.
EODisplayGroup provides an abstraction of a user interface,
comprising of an ordered collection of data objects, some
of which are displayed, and of those some are selected.
Handles notifications from the data source's editing context,
looking for InvalidatedAllObjectsInStoreNotification and
ObjectsChangedInEditingContextNotification, refetching in
the former case and updating displayed objects in the latter.
Overridden to intercept notifications of changes to objects
in the controlled display group and broadcast a change on the
parent group's selected object.
Writes the specified value for the display group
and key currently bound to the specified aspect,
at the specified index (assuming it's an indexed
property).