> Also resolve_example_ordering seems like it could just be named #[] -- to me, the registry has similar semantics to a hash and I'd expect to be able to look up an ordering strategy using the square bracket method.

I just realized you've named it as such because of the separate example and group ordering.  A suggestion: consider using a separate `OrderingRegistry` instance for examples and a separate one for groups.  To me, the example/group split fits better as a separate instances and not as part of the interface of the registry itself.  If you move in that direction, then it would become natural to use `#[]` as the lookup method.

Thoughts?