referencing IDNA2008 (and IDNA2003?)

Patrik Fältström patrik at
Fri Oct 22 04:36:54 CEST 2010

I completely agree, and fwiw people not really into the details of IDNA2003/IDNA2008 details should note what people sort of have said between the lines, with IDNA2008, it does not really matter whether A-label or U-label is in use, while in IDNA2003 you really wanted to use what in IDNA2008 is called A-label.

And the incompatibilities when you look at this is really only in two codepoints, final sigma and the sharp-s.

Something that I personally think is a "bump in the road" that will be handled (and is handled) by registration policy, which also will go away faster in reality than what we might be nervous about in theory.

My suggestion is because of that also something like "use A-labels when comparing and storing strings in cookies". Done.

Do not invent your own algorithms.

It is much easier to then iron out the potential issues as real issues as both the real issues _and_ mistakes in the design of the tailored algorithm. Which unfortunately most likely will be greater than zero. Regardless of how hard we work.


On 21 okt 2010, at 19.22, Vint Cerf wrote:

> i am a big fan of the canonical A-label form for all comparison and
> processing purposes, converting to U-label format when display is
> needed.
> vint
> On Thu, Oct 21, 2010 at 6:21 PM, Andrew Sullivan <ajs at> wrote:
>> On Thu, Oct 21, 2010 at 05:45:51PM -0400, John C Klensin wrote:
>>>       (2) The application insists that all IDNs, including
>>>       especially what is stored in cookies, use A-labels and
>>>       then behaves in a fashion that is as ignorant as
>>>       possible as far as details & versions of IDNA are concerned.
>> I will note that my personal preference is very much this option.  I
>> think it would be an excellent idea to suggest that this is the best
>> option, because it's the most interoperable (IDNA-ignorant systems
>> don't spit up on it, for instance), because it's always possible to
>> get the U-label back out, and because it means that you do the
>> A/U/A/U-label dance only one time, at the end, when it's time to
>> display.  But if people are going to put U-labels anywhere, I agree
>> with John that the best advice we can give is "follow the rules".
>> A
>> --
>> Andrew Sullivan
>> ajs at
>> Shinkuro, Inc.
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