Expanding means bringing into view any subentities associated with an
     entity.  Collapsing means taking those subentities away from view.
     A highlighted icon (a dark diamond) in front of an entity or subentity
     indicates that it has children and may be expanded or collapsed.  For
     example, when you expand the Node entity, its subentities, such as
     Event Dispatcher, Alias, etc. will appear.