Stupid U-label question [correction]

[Vint Cerf]

the definition of A-Label is deliberately not recursive; that helps.

On Aug 20, 2008, at 7:46 AM, Frank Ellermann wrote:

> Tina Dam wrote:
>
>> A domain name cannot begin with "xn--" unless it is an A-label.
>> Your "u2" below is not an A-label as far as I can tell.
>
> Yes, based on an IDNA2003 rule and the "--" rule in John's draft.
>
> If he'd remove the "--" rule instead of replacing it by something
> better xn--4caä could be an U-label, after all it's LDH plus one
> perfectly PVALID umlauted a.
>
> And if xn--4caä *would* be an U-label, then it *would* follow that
> xn--xn--4ca-cxa is an A-label (and vice versa).  Of course nobody
> here wants this.  An obscure corner case, maybe useful as example.
>
>  Frank
>
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