Re: idna-bis and '〓'

Martin Duerst duerst at
Tue Nov 27 05:04:18 CET 2007

At 22:03 07/11/26, John C Klensin wrote:
>--On Monday, 26 November, 2007 13:20 +0100 Harald Tveit
>Alvestrand <harald at> wrote:
>> --On 26. november 2007 12:53 +0100 Thomas Roessler
>> <roessler at> wrote:
>>> On 2007-11-23 19:16:43 +0100, Harald Tveit Alvestrand wrote:
>>>> It's an user interface issue what to do when the user types
>>>> a LATIN SMALL LETTER SHARP S; idnabis deliberately does not
>>>> require that one maps it to "ss".
>>> It is *not* a user interface issue what to do when an IRI is
>>> encountered that includes that latter.  If I understand you
>>> correctly, that behavior is currently undefined in idnabis.
>> Yes, that is a problem with the IRI spec.

I was extremely surprised to see that. Not so much because
I'm one of the authors of the IRI spec; paper and electrons
suffer a lot of blame without much damage.

What I'm surprised is the lack of understanding and responsibility
when proposing making potentially wide-reaching changes to a spec.
What idnabis does is to change the rules for non-ASCII domain
names. Up to now, a sharp s in a domain name was mapped to 'ss'.
With idnabis, such a sharp s is simply 'a user interface issue'.

Independent of whether mapping in idna2003 was a good idea
or not, what the above change does is to just leave some
domain names foat in the air.

Imagine, as an equivalent, if a new version of the domain
name spec suddenly abolished case-sensitivity, and made that
a 'user interface issue'. Nobody would come and claim that
it's simply a problem of specs using domain names that there
is no longer a guarantee for e.g. WWW.IETF.ORG to resolve.

Also, imagine somebody with a domain name with a sharp s
on their name card. According to your logic above, the fact
that this domain name no longer is guaranteed to resolve
would simply be a problem with the name card spec? Wouldn't
the carrier of this business card think that's a problem with
idnabis, which suddenly pulled the rug under what idna2003
declared to be a perfectly fine, legitimate domain name?

The URI community, and the URI spec (yes, URI, not IRI) has
long had a clear understanding that URIs have to work not
only over electrons, but also on things such as napkins
and the side of a bus. For domain names, I think such an
understanding was never made quite explicit, but it is
nevertheless a very strong assumption in the way we currently
use the (ASCII-only) DNS. It may be time to be more
explicitly aware of this assumption. When things have
to work on business cards and the like, simply saying
that something is a user interface issue doesn't cut

>Put differently, to the extent to which IRIs specify a user
>interface behavior, it would be perfectly reasonable for the IRI
>spec to specify that SHARP S should be mapped to some other
>character or character sequence ("ss" by the orthography rules
>of some German-speaking countries, "fs" by appearance, "ナソs"
>(U+017F U+0073) by origin, etc.

My guess is that the IRI spec would just say that there are some
domain names that have been guaranteed to work under idna2003,
but no longer are guaranteed to work under idnabis, so these
should be avoided. The URI spec and the IRI spec have traditionally
avoided to meddle with the details of identifiers they include.
One reason for this is that URIs and IRIs may contain domain
names e.g. in query parts, where they cannot be idenified as

Another issue I guess is that if indeed idnabis had strong
reasons to avoid mapping (such as the fact that it makes
it difficult to update tables for new versions of Unicode),
then such reasons would also apply to the IRI spec.

>Certainly, if it is to be
>mapped to anything but itself, that needs to be specified.  But
>it should not be an IDNA problem, especially since IRIs might
>choose to map it differently in different contexts (I don't need
>to remind either of you that tails are case-sensitive so the
>IDNA2003 rules don't apply).

I don't understand what you mean by 'tails'.

And I clearly think that idna, and not any other spec, should
say what to do and what not to do for internationalized domain
names. IRIs, like business cards, are only a carrier.

Regards,    Martin.

#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#       mailto:duerst at     

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