Backwards compatibility

Simon Josefsson simon at
Tue Mar 18 20:26:01 CET 2008

"Mark Davis" <mark.davis at> writes:

> I agree. The main backward compatibility change is that without
> preprocessing a very number of strings break. If someone does do
                       ^ I assume 'small' or similar
> preprocessing -- and we define a uniform mechanism for doing it -- then the
> differences can be quite small (depending on what the wg decides).
> For more information on possible preprocessing, see the rough draft at* **
> *.

I think the pre-processing section contains some good ideas, and may
describe roughly what MSIE/Firefox actually implements, which is better
than what's in IDNA2003 today.  Have you considered turning the section
into an IETF draft?  To be able to offer MSIE/Firefox-compatibility in
libidn I would implement a draft like that.


> Mark
> *
> On Tue, Mar 18, 2008 at 9:44 AM, Simon Josefsson <simon at>
> wrote:
>> Harald Tveit Alvestrand <harald at> writes:
>> >> I'm assuming IDNABIS won't be (fully) backwards compatible with
>> >> IDNA2003.  That is the impression I have gotten from all discussions so
>> >> far.
>> > The only incompatibility so far proposed is that some names valid
>> > under IDNA2003 will not be valid under IDNA200x, and vice versa. For
>> > all names that are valid under both proposals, I don't believe any
>> > change has been proposed.
>> When you upgrade the Unicode version, some strings that normalize to one
>> value under Unicode 3.2 NFKC will not normalize to the same value under
>> Unicode 5.0.  See:
>> I have also noted the discussion around ß.  If IDNABIS-ToASCII(ß) != ss
>> then another backwards incompatible change is made.
>> In my comment on the IDNABIS WG charter I suggested that the charter
>> should say that the IDNABIS output needs to be strongly backwards
>> compatible.  Both Lisa and Sam from the IESG disagreed.  My conclusion
>> is that the WG is entitled to make backwards incompatible changes, and
>> given the discussions so far that involves using Unicode > 3.2 NFKC and
>> how ß will be handled, the WG will likely also make backwards
>> incompatible changes.
>> I think a useful output from the WG would be to clarify which backwards
>> incompatible changes are being made.
>> /Simon
>> _______________________________________________
>> Idna-update mailing list
>> Idna-update at
> -- 
> Mark
> _______________________________________________
> Idna-update mailing list
> Idna-update at

More information about the Idna-update mailing list