Casefolding Sigma (was: Re: IDNAbis Preprocessing Draft)

Martin Duerst duerst at
Fri Jan 25 09:48:59 CET 2008

[I'm sorry for the delay in answering some of the messages
due to other urgent duties (term-final exams).]

At 04:51 08/01/23, John C Klensin wrote:

>Nothing prevents their "using final sigma".  Under IDNA2003,
>they can "use" it, but it is case-mapped to lower case sigma.
>Once that mapping occurs, they can't get it back, but I suppose
>that is different from not being able to use it.

Whether it's different or not depends on the definition of use,
but I'm sure that users will see it that way: They can't use it
in the way they usually would.

You have, in earlier mail, pointed out that this kind of behavior
is confusing to users, and I think you also have given that
confusion as one of the reasons for the need of work on IDNA.

>IDNA200X, as proposed, their localized software can map it to
>lower case sigma before getting to IDNA and can, if desired, map
>any sigma character in a final position into the final form on
>the way from the ACE form to the native character one.

At first sight, that may make sense. But we currently have absolutely
*zero* experience with what's subsumed here under the term
'localized software'. In very general terms, it's an user interface
issue, and the IETF as such has been known to not be specialized in
such issues.

Also, it creates a totally unnecessary difference between how
IDNs have to be dealt with and how other text is dealt with.
Any such difference will mean confusion to users and additional
work for implementers.

Regards,    Martin.

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

More information about the Idna-update mailing list