Re: [idn] ToUnicode output can be longer than input

[Dan Oscarsson <Dan.Oscarsson@kiconsulting.se>]

Adam M. Costello wrote:

>An ACE label is formally defined as a label that ToUnicode would alter.
>A (valid) internationalized label is formally defined as a label to
>which ToASCII can be applied without failing.  It can be shown that all
>ACE labels are (valid) internationalized labels.

No that is wrong.

A IDNA ACE label is defined as above. Not ACE in general.
An internationalized label might be an ACE label, but is only
defined by ToASCII within IDNA. In general a domain name (including
all so called internationalised) do not require the IDNA ToASCII
to work. There are several domain names that will fail when ToASCII
is used, but are still domain names. They just cannot be handled by IDNA.

While this discussion is focused on IDNA, IDNA do not define thw world
and do not define the basic semantics of ACE or domain names with non-ASCII
characters. IDNA does only define a way to encode domain names so
they can be sent over lagacy ASCII DNS protocol. It does not define
what domain names work in an international context.

   Dan