Allows to exclude nodes from being added to the object graph based on criteria that are only known after the diff
for
the affected node and all its children has been determined.
Currently it is only possible to configure returnability based on the state (_added_, _changed_, _untouched_, etc.)
of the `DiffNode`. But this is just the beginning. Nothing speaks against adding more powerful options. It would be
nice for example to be able to pass some kind of matcher to determine returnability based on dynamic criteria at
runtime.