Punycode & IMA/EAI

[Patrik Fältström]

On 22 maj 2008, at 15.05, John C Klensin wrote:

> --On Thursday, 22 May, 2008 21:46 +0900 Felix Sasaki
> <fsasaki at w3.org> wrote:
>
>> ...
>> Am I right in the assumption that the *if* there is need for
>> Powder to have 100% reversibility of mapping U-label <>
>> A-label, this could be guaranteed with IDNbis as currently
>> planned, but not with IDN2003?
>
> Mostly yes.   For IDNA2008, one would simply have to enforce a
> "no mapping" rule in the application (external to IDNA itself).

I would like to state this differently.

For IDNA2008 the definition of A-label and U-label is such that there  
is a 1:1 mapping between them.

If we get a mapping step being part of IDNA2008 (see Mark's proposal),  
then my view is that we will have a few different labels:

1. A-label -- What is registered in DNS, 1:1 mapping to U-label
2. U-label -- 1:1 mapping to A-label
3. I-label -- A string in Unicode that via proper defined mappings  
turn (non-reversably) into a U-label
4. Non-valid A-labels -- things that start with "xn--" that are not  
valid
5. "Not even I-labels" -- thing in Unicode that are not an I-label

Or something.

I.e. when mappings are added to IDNA-2008, I do not want the mapping  
to extend the set of U-labels, but instead define a new label.

    Patrik