A-label definition

[Frank Ellermann]

Mark Andrews wrote:

> At best there is guidance not to allocate a TLD which will
> potentially clash with a representation of a IPv4 address.
 
> 0xde.0xad.0xbe.0xef
> 222.137.190.239
> 0xdeadbeef
> 0337.0211.0276.0357
> 033653337357
> 3735928559

The 0x concept would break various of my scripts based on 
"if it only contains the characters '0.123456789' it might
 be an IPv4, and it is no FQDN (or vice versa)".  

Maybe it is a good idea to say that  "0x" 1*HEXDID  cannot
be a <toplabel>, but that has to be said in something that
is fresher than "RFC 952 - status: unknown".  With no note
about "updated by RFC 1123".

> xn--* will never clash with a dotted decimial or any other
> representation of a IPv4 address.

Yes, any valid A-label is automatically a valid <toplabel>.

> xn--* is a legal tld under RFC 952 and it was not made
> illegal by RFC 1123.

RFC 952 has a limit of 24 characters and proposes suffixes
like "-GW" and "-NIC", let's say it was not designed for
IDNA and RFC 3492.  If you think it helps we could move
RFC 952 to HISTORIC, it muddies the water when it shows up
in ICANN documents published in 2008.

The decruft experiment (RFC 4450) missed RFC 952, because 
it was limited to standards, excluding "status: unknown".

 Frank