Punycode & IMA/EAI

Felix Sasaki fsasaki at w3.org
Mon May 26 01:32:21 CEST 2008

Thank you for this explanation, John, that is very helpful. I will bring 
that back to the W3C i18n and Powder folks and see if a follow-up is needed.


John C Klensin さんは書きました:
> --On Thursday, 22 May, 2008 21:46 +0900 Felix Sasaki
> <fsasaki at w3.org> wrote:
>> ...
>> Am I right in the assumption that the *if* there is need for
>> Powder to have 100% reversibility of mapping U-label <>
>> A-label, this could be guaranteed with IDNbis as currently
>> planned, but not with IDN2003?
> Mostly yes.   For IDNA2008, one would simply have to enforce a
> "no mapping" rule in the application (external to IDNA itself).
> For IDNA2003, since the non-reversible case and compatibility
> mappings are integral to the protocol, one can, strictly
> speaking, not do that.
> _However_ note that enforcing a "no mapping" rule in the
> environment surrounding IDNA2008 invocations gives up some
> compatibility with expectations for IDNA2003 strings.  We have
> some statistics (posted by Mark to this list earlier, I think)
> about how many existing names in references, as seen by Google,
> are dependent on the IDNA2003 mappings.   We have no real
> information about how strong the expectation of mapping is held
> in the community (although there are many strong opinions).
> Conversely, one could effectively reverse-engineer IDNA2003,
> applying the Nameprep mappings as a canonicalization method
> before applying IDNA.  If one did that, IDNA2003 would be, for
> this purpose, roughly equivalent to IDNA2008.  But one would
> need to be sure that any domain names used in or with Powder
> were in that reduced form, rather than the more permissive forms
> permitted by IDNA2003.
>     john
> bbb
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