Comments on draft-ietf-idnabis-defs-10

Paul Hoffman phoffman at
Thu Sep 3 01:51:04 CEST 2009

At 1:21 PM -0400 9/2/09, John C Klensin wrote:
> > 1. Symmetry constraint between U-label and A-label is a
>> desirable property and key design goal of IDNA2008
>> 2. A-labels, being a subset of LDH-labels are sometimes stored
> > and used without preserving case.

I'm a little leery of this point. It assumes that the A-label was derived from a U-label or was produced by checking the U-label equivalent, not just "a desirable property". We need to either beef up point 1, or elucidate point 2 more.

> > 3. When that happens, we end up with having uppercase
> > characters in the Punycode decoded result, which makes it an
> > invalid U-label.

...we *can* end up with having...

> > 4. This happens because of the Punycode
>> algorithm preserving the cases of the "basic code points" in
>> the decoding process.

...algorithm possibly preserving...

> > 5. Because the Punycode encoding process (practically) never
>> outputs uppercase characters from valid U-labels, we know that
>> a valid A-label must not contain any uppercase character after
> > the "xn--" ACE prefix.

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