There are 2 situations here (perhaps should be listed separately)

1. If I configure some collection as a leaf node, I want to be alerted of a change when the size of the collection changes but I do not want to be told if anything in the collection has changed.
2. If I am comparing objects of type A (which has a property named "b" of type B, which has various properties), I want to be able to configure "b" as a leaf node, so that if an property under b changes, the difference reported is that b has changed, rather than the property beneath b.