Stupid U-label question [correction]

[Frank Ellermann]

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