t is, the serialization trait implementation
level <= object_serializable.
<li>Tracking for this type is set to "track selectively"
in this case, indication that an object is tracked is
not stored in the archive itself - see level == object_serializable.
Since class information is not saved in the archive, the existence
or absense of the operation ar << T * anywhere else in the 
program is used to infer that an object of this type should be tracked.
<p>
A problem arises when a program which reads an archive