Versioning policy for Internal modules

[maoe]

It's been a common practice in the Haskell community to put internal functions to Internal modules, which are not meant for a public API but for a semi-private API that can be useful to access library internals to extend the API. I think it's natural to relax the versioning policy for changes in those Internal modules. Should we mention it somehow in the PVP?

[hvr]

Yeah, I think it makes sense to formalise this, as I'd like PVP-validation tooling to be able to be aware of that kind of convention