I don't think so actually, as that would preclude ASCII or UCS ranges, or "special ranges" that don't return characters at all. All we really do care about is if it is possible to compare the elements of the range, with `dchar` (like the statement says).

Another example, a range of `CaseInsensitiveDchar` would need to work too.

That said, do note that since `char.init` is `0x10FFFF`, if `opEquals` doesn't accept (at least) a `dchar`, then it *will* get refused.