Allows a sub-element of a complex element to notify its parent element that it has been changed. 

The notification algorithm works the following way:

• The call of the method close() of the sub-element object triggers a modification notification handler, which calls the xmitPropagateModify() method.
• The sub-element object calls the recvPropagateModify() method of its parent element and passes to it the pointer to itself.
• The method recvPropagateModify() of the parent element sends a modification notification to the top element of its class hierarchy.

The default implementation of this function does nothing. This function can be overridden in custom classes.