Stupid U-label question [correction]

[William Tan]

>> | Let u2 = xn--4caä, and use punycode *directly*
>> | to bypass the RFC 3490 4.1 (5) restriction.
>> |
>> | That results in A-label xn--4ca-cxa.  Therefore
>> | in theory u2 could have A-label xn--xn--4ca-cxa
>> | IFF that is not prohibited somewhere in IDNA200X.
>
> "xn--xn--4ca-cxa" is a resolvable LDH label. Under IDNA2003, it will
> not get converted by ToUnicode because it will fail Step 6 of RFC3490
> Section 4.2 (running it through ToASCII).
>

Let me clarify:

ToASCII("xn--4caä") will fail.
ToUnicode("xn--xn--4ca-cxa") will result in itself "xn--xn--4ca-cxa",
though we don't know or care how it was produced. All we know is that
it does not come from a valid U-label.

=wil