Changing the xn-- prefix

James Seng james at
Tue Mar 25 12:52:13 CET 2008

I remember xn-- was selected after exhaustive data mining on .COM zone
file back then and in the process, we found a few others that could be
use. "xn" basically was then pick "randomly".

I agree that there are complexity to change xn at this moment.
However, I am not totally against changing the prefix if the following
conditions are fulfill

a) there is a STRONG technical reason that a new prefix is needed

b) there must be backward compatibility with all existing IDN labels
with xn prefix.

For example, and I am not making any proposal, this is really just
merely an example, that I would consider a change of prefix if it we
agreed the best way to identify IDNA vs IDNA200X labels is via the
prefix (and I do not necessary agree at this moment) and that no
IDNA200X labels with a new prefix can be de-constructed to an xn--
IDNA label, ie the round-trip conversion between IDN and ACE labels
must always be consistent.

Much of the above are already captured somehow in Section 9.3 of the
issue document.

Perhaps lets not to mention the prefix change is allowed or disallowed
in the charter and let the working group sort it out.

-James Seng

On Tue, Mar 25, 2008 at 2:29 PM, YAO Jiankang <yaojk at> wrote:
>  ----- Original Message -----
>  From: "Patrik Fältström" <patrik at>
>  To: "Shawn Steele" <Shawn.Steele at>
>  Cc: <idna-update at>; "John C Klensin" <klensin at>; "Mark Davis" <mark.davis at>
>  Sent: Tuesday, March 25, 2008 10:23 AM
>  Subject: Re: Changing the xn-- prefix
> > On 25 mar 2008, at 00.13, Shawn Steele wrote:
>  >
> >> I reread your original mail, and in particular I don't want to get
>  >> bogged down in the debate of details while trying to set the
>  >> guidelines, but I'd like to try for "A prefix change MUST be
>  >> avoided" (removing the condition).  If that's going to cause too
>  >> much randomization, then I'd back down, but the repercussions of
>  >> changing the prefix are huge.
>  >
> > I am personally in favor of text in the charter that say "The prefix
>  > xn-- MUST NOT be changed." where MUST NOT is defined according to the
>  > IETF definition in RFC 2119 (
>  +1
>  > This put a constrain on the changes the wg is allowed to do to
>  > IDNA200X (not large so that the prefix has to change) -- at least not
>  > without rechartering.
>  >
>  >    Patrik
>  >
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>  >
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