Generally new features in protobuf are just new features, so if a new feature is added then the worst case is the documentation will be out of date/incomplete f

Generally new features in protobuf are just new features, so if a new feature is added then the worst case is the documentation will be out of date/incomplete for a short period of time. For the most part the "constraint tightening" thing doesn't affect the language specification, at least in my experience. For example, there have been some changes in protobuf that affect things like serialization order. A change like that can break brittle tests that do things like checking that a function produces some exact serialized string/byte sequence, but they don't affect the semantics of the language.