Comments on draft-ietf-idnabis-defs-10

[Patrik Fältström]

On 31 aug 2009, at 08.06, John C Klensin wrote:

>> 2.5. LDH (E) E:
>>
>>     cp is in {002D, 0030..0039, 0041..005A, 0061..007A}
>
> But that would be a mistake, IMO, because it would result in
> U-labels containing uppercase ASCII that produce different
> A-labels from the same U-label with lowercase ASCII.  Those
> A-labels would match in the DNS, which uses case-insensitive
> comparison, but not in ordinary string comparisons (because they
> are different).

I think I agree with your conclusions, but I have some issues with  
your arguments.

But that is how domain names must be handled today. So this is nothing  
new.

klensin and KlEnSiN are to be "the same".

> Put differently, that would give us a pair of U-labels that do
> not compare equal on bitstring comparison (the only kind of
> comparison defined for U-labels) but which produce equivalent
> (although not identical) A-labels.

This I agree is the key argument.

We do NOT have bitstring comparison for domain names today. But we  
require it in the future.

> And, because of the
> compression "feature", we would lose unambiguous symmetry of
> A-labels and U-labels because, depending on where it came from,
> a given A-label (and its DNS-equivalents) could produce
> different U-labels.

Here you use the term "different", and I think we should concentrate  
on that.

> This would also imply that
>   "Fältström" and "fältström"
> would be valid U-labels but that "FÄLTSTRÖM" would not be
> because Ä and Ö are both DISALLOWED.  I don't think we want to
> go there.

Understood and accepted.

    Patrik