Notification function called each time an Undo operation is performed this object is using partial Undo. 

An object indicates it's using the partial undo mechanism, if and only if it has set autoUndo false in all calls to assertWriteEnabled(). 

This member function must know which types of fields to scan, and must stop after reading what it it needs. 

If the class type specified by pClassObj does not matches the class of this object, this member function must call the parent class's applyPartialUndo() and return whatever it returns. 

If it does match the class of this object, this member function must use pUndoFiler to read the undo data, then typically use this object's set() method.