Greek Casefolding sigma

Patrik Fältström patrik at
Sat Mar 29 10:00:07 CET 2008

On 28 mar 2008, at 18.52, Mark Davis wrote:

> That would show
> σωτήρης properly, and maintain compatibility.

This is not about how to "show" things, as DNS is nothing else than a  
storage / lookup mechanism.

You store a key, and together with that key some data. You can _NOT_  
send in the data and get the key back.

The way IDNA2003 is designed is that the key does _NOT_ allow final  
sigma, and this because of design of Unicode. Regardless of if "the  
user typed" sigma or final sigma, the same key should match. Without  
changing the matching algorithm (that is out), the key have to be  
calculated on the client side. This key that is sent in is sigma,  
never final sigma.

There is _no_ "reverse" mapping in DNS. Just lookup.

That said, one can do a lookup of a PTR record where the data is a  
domain name. This domain name because of same rules as for the key can  
not include the sigma, but the final sigma. And if that is the problem  
people try to resolve, then that is what should be discussed, but that  
has not much to do with the creation of the key used in the lookup.


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