I've been more specific about `validate_hash` [here](https://github.com/alphagov/vcloud-core/commit/5ad9a0e26fc2dc8259c1a1123d0d2370cb74dea7#diff-6a1bb510b89f6604c96c8817a62162b6R17); it does recurse, just indirectly via `check_hash_parameter`.

Maybe it'd be more helpful for me to remove these inline method comments and rely on the class comments at the top?