Objects derived from the abstract base class AcDbObjectContext can represent a particular context which may affect the behavior of objects; in this case, annotation scaling. Applications implement AcDbObjectContextCollection to define custom object contexts; they must also register this instantiation with AcDbObjectContextCollectionManager.
Current contexts can be set by invoking AcDbContextColleciton::setCurrentContext(). Be sure to create an AcDbContextCollectionIterator object to interface with the collection.