Comments on draft-ietf-idnabis-defs-10

[Andrew Sullivan]

On Mon, Aug 31, 2009 at 11:46:19AM -0400, John C Klensin wrote:

> Actually, if they are the output of a Punycode conversion from a
> valid U-label, then they are lower-case (except possibly for the
> prefix, which makes no difference).   In that sense, the
> proposed prohibition is just a reminder that A-labels containing
> significant upper case characters are impossible... no new rule
> at all.

This is what I've been trying to determine.  

As far as I can tell, for IDNA-aware applications, no U-label that has
an upper case ASCII character in it can possibly be looked up, because
protocol says

   Putative labels with any of the
   following characteristics MUST BE rejected prior to DNS lookup:

[…]

       o  Labels containing prohibited code points, i.e., those that are
      assigned to the "DISALLOWED" category in the permitted character
      table [IDNA2008-Tables].

And tables says that the upper case characters are DISALLOWED, so
everything is fine.  If that's right, then I'm not sure why we need to
change anything.  If the worry is that some non-conforming application
will look these up without being careful, so what?  We can't make
special rules for non-conforming applications, because they're
non-conforming.

A


-- 
Andrew Sullivan
ajs at shinkuro.com
Shinkuro, Inc.