Backwards compatibility (was: Re: Wwhich RFCs the new work would obsolete, vs update or leave alone)

Mark Davis mark.davis at
Tue Mar 18 19:25:54 CET 2008

I agree. The main backward compatibility change is that without
preprocessing a very number of strings break. If someone does do
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* ***<>

On Tue, Mar 18, 2008 at 9:44 AM, Simon Josefsson <simon at>

> 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
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