@drasmuss Maybe `__mro__`... I'll give this a bit more thought as I rebase to master with the defaults system merged in.

@bcipolli @studywolf I don't think I was there for the assert discussion, but I think you're right @bcipolli, asserts are more appropriate for these types of errors that backend developers would get. I don't think we've been programming this way thus far, but I'll try to do it that way from now on :)