Re: [idn] Who supports UDNS (ACE+UTF-8)

["Adam M. Costello" <amc@cs.berkeley.edu>]

"Eric A. Hall" <ehall@ehsco.com> wrote:

> I think that it is probably also feasible to adopt a "continuation"
> syntax in ACE as part of a backwards compatibility.

This has been proposed before.  It's certainly a clever idea, but
it's not clear that it wouldn't create more compatibility problems.
Applications sometimes pay attention to the number of components in a
domain name (the web cookie protocol is one example), and sometimes
chop them up.  If the name appeared to have a different number of
components when viewed by an IDN-aware application versus an IDN-unaware
application, there could be subtle interoperability problems.

Consider an IDN FOOBAR.org whose ACE is ace1.ace2.org.  An application
might be faced with the question of whether FOOBAR.org is a subdomain of
ace2.org.  Is there a right answer?

The nicest thing about the ACE approach is that it obviously breaks no
software or protocols.  That would no longer be obvious if continuations
are possible.  My get feeling is that it would be more trouble than
it's worth, but if you want to pursue this, please try to work out some
semantics that are consistent and demonstrably safe.

AMC