Comments on draft-ietf-idnabis-defs-10

"Martin J. Dürst" duerst at
Wed Sep 2 05:03:37 CEST 2009

On 2009/08/31 6:37, Paul Hoffman wrote:
> Wil is correct, and this is clearly called out in RFC 3492:
>     Punycode can also support an additional feature that is not used by
>     the ToASCII and ToUnicode operations of [IDNA].  When extended
>     strings are case-folded prior to encoding, the basic string can use
>     mixed case to tell how to convert the folded string into a mixed-case
>     string.  See appendix A "Mixed-case annotation".
> We hated it at the time, but Adam insisted on leaving it in.
> If we want the output of Punycode to be all lower-case, we have to covert it after the conversion ourselves.

Couldn't we just say "use punycode, but without Appendix A"? It seems 
that that's what implementations are doing, anyway. I don't think this 
is able to deal with simple US-ASCII characters, but it will deal with 
potential upper-case letters in punycode that represent non-ASCII 

Regards,   Martin.

#-# Martin J. Dürst, Professor, Aoyama Gakuin University
#-#   mailto:duerst at

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