> Just because the interface is modelled after enumeration types, it
doesn't mean that there is (or should be) an enumeration type behind.

"Is" is correct, but the API is there and would be useful if one could
use it. An enumeration type could implement endianness? like here, it
could list all endiannesses (for testing, for example, or for
advertising options for the user to select), it could use sets to
advertise known endiannesses for certain operations (using
enum-set-projection and other operations), etc. Some operations might be
niche, but the enumeration type system is there already and gives you
them for free. It would make perfect sense to use it. (Integrating the
enumeration system into other libraries would also make it seem less
tacked-on.)

-- Peter McGoron