Changing the xn-- prefix

Andrew Sullivan ajs at
Wed Mar 26 18:12:44 CET 2008

Dear colleagues,

On Wed, Mar 26, 2008 at 05:45:47PM +0100, Simon Josefsson wrote:

> IDNA200x could say that each old name has to be registered under the new
> prefix as well, and then both new and old implementations will find it
> without problem.  It would thus be possible to implement IDNA200x
> without IDNA2003 in a client and have it work.

As I think I already argued, it is my belief that any explicit
requirement that IDNA200x imposes IDNA2003 compatibility is a bad
If IDNA200x still requires all the current IDNA2003 complication, then
registries and client developers will quite correctly wonder what the
big benefit is supposed to be to them.  So they'll resist implementing
the new standard.

Moreover, keeping such a requirement entails that we will live forever
with IDNA2003.  People who are now unhappy that they're not
accommodated in IDNA2003 will instead be unhappy that they're
"second-class" because their script doesn't work with all the software
out there (including that stuff that won't implement all of IDNA200x
because "we implement the backward-compatible portion").

I think any explicit attempts to make full backward compatibility a
requirement would be a bad idea.  Some things are going to break, and
we will have to accept that.  It's a good incentive to get this work
completed quickly, before even more possibly problematic cases can be

Best regards,


Andrew Sullivan
ajs at
+1 503 667 4564 x104

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