There are other tests where we could use `HasFlag()` (or `HasAny<>()`) too. From a purity standpoint, they really don't belong as part of the public surface area of a Git library, but is that a good enough reason? Or there's the slippery slope of `[InternalsVisibleTo]`, which would allow `Core.Epoch` and the public classes in `Core.Compat` to be hidden.