Document methods of class IArray

There is almost no documentation for class IArray. E. g., what is the semantics of unsafeArray and how unsafe is it?

I see that Data.Array.Base is documented as internal, but it's the only module exporting methods of IArray and so anyone defining their own instances depend on it. Lack of documentation means that users will be at loss how to define an instance (and likely to define something violating array expectations).