Casefolding Sigma (was: Re: IDNAbis Preprocessing Draft)

Patrik Fältström patrik at
Mon Jan 28 20:17:55 CET 2008

On 28 jan 2008, at 16.12, Vaggelis Segredakis wrote:

> Some people on this list propose this should change. Can you please  
> clarify
> your proposal on this issue and be as kind as to explain to us  
> Greeks why
> the previous solution creates problems to your protocol?

In IDNA2003, U+03C2 was as you say mapped to U+03C3. This implies that  
whenever someone entered U+03C2 (regardless of position in the label),  
the U+03C2 was first mapped by Nameprep to U+03C3, and then U+03C3 was  
registered in the DNS (after conversion to ASCII of course).

If we take this to IDNA200x, we see that already in IDNA2003, U+03C2  
was not allowed in what we in IDNA200x call U-label.

My conclusion after seeing the discussions on this list is that we  
should keep this requirement, that U+03C2 is not allowed in the DNS,  
i.e. that it get the derived property value NEVER. It gets NEVER as  
casefold(U+03C2) != U+03C2.

I looked through through presentation on DNAME and bundling, and I  
thank you for the hard work you have put into this. I will keep the  
presentation as one that one should read many times. I might come back  
with questions later.

    Regards, Patrik

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