Stability of valid IDN labels

[Stephane Bortzmeyer]

On Fri, Apr 18, 2008 at 02:34:02PM -0700,
 Eric Brunner-Williams <ebw at abenaki.wabanaki.net> wrote 
 a message of 41 lines which said:

> The requirements for labels arises somewhere, and I suspect that for
> the IETF's IDN activities, past and present, the author of that
> requirement is, at in part, ICANN, [...] If that is the origin of
> the requirement for stability

I do not care about what ICANN says or does not say but let me say
that stability is important for a lot of people, whatever such or such
organization may think.

> Please consider the 3166 code points

There is a huge difference: to know if a two-letter TLD is currently
valid or not, you perform a DNS lookup. If a new two-letter TLD is
added or deleted, all the resolvers on earth will see the change
immediately (minus DNS TTL and various delays in propagation). So,
changing the status of two-letter TLD raise no technical issues. (As
mentioned by John Klensin, some software use a hardwired list of TLD,
but they are so broken that they are probably not worth mentioning.)

In IDNAbis, no lookup is done for a poor character which has been
classified as invalid. So, an invalid character will never be able to
become valid (without changing all the resolvers in usage). That's why
stability is a different issue than it has always been with DNS. (The
example of the language tag registry, given by Mark Davis, is a better
one, since language tags processors are not supposed to do online
validation, so, for language tags, stability is necessary.)