[idn] nameprep allows Alpha?

["D. J. Bernstein" <djb@cr.yp.to>]

I'd like to draw more attention to this example from Dan Oscarsson,
because I find it extremely worrisome.

According to Paul's nameprep script, uppercase Alpha Beta is accepted in
domain names, and matches lowercase alpha beta, not ab.

But uppercase AB---which, when properly displayed, has the same glyphs---
matches ab, not alpha beta.

I thought the point of nameprep was to prevent confusion: in particular,
to guarantee that two valid host names will match inside the computer if
they match visually. If Alpha Beta and AB are valid, they have to match.

Paul Hoffman / IMC writes:
> > > http://www.imc.org/nameprep
> > Is that (1) up to date and (2) normative?
> (2) What do you mean?

The final nameprep specification should be working software; anything
else is unnecessarily error-prone and unnecessarily difficult to review.
My question is whether your software is the current specification.

---Dan