Prohibiting mapping of PVALID characters
"Martin J. Dürst"
duerst at it.aoyama.ac.jp
Thu Dec 10 08:02:35 CET 2009
I think the confusion you talk about below comes from the fact that
PVALID is defined on single characters, but NFC (as a form) is defined
on sequences of characters. What we require for U-Labels (among else) is
that they only contain PVALID characters AND that they are in NFC. The
only effect that applying NFC (as a conversion) can have for a sequence
of PVALID characters is that it may create a sequence that contains
PVALID only but is not in NFC into a sequence that contains PVALID only
but is also in NFC. The former isn't an U-label, the later is.
[For everybody, I think it's important to understand that (as far as I
know, Ken or Mark please correct me if I'm wrong), none of the two (to
four) characters we are currently wrestling with is in anyway involved
Here are some additional things that we might want to check just to be
sure we understand things:
a) There may be sequences of PVALID and not PVALID characters, than when
applying NFC, turn into sequences of PVALID only. If there are such
cases, I think they should be allowed, and our text shouldn't forbid
such a transformation.
b) There may be a way to apply NFC to a sequence of PVALID characters
only and the result would contain some non-PVALID characters. If that's
the case, those characters might further be mapped to something; would
we be okay with that?
On 2009/12/10 13:05, Andrew Sullivan wrote:
> On Wed, Dec 09, 2009 at 05:10:42PM -0800, Kenneth Whistler wrote:
>> I repeat: strings do not turn into NFC form by magic. They
>> are mapped by the normalization algorithm. And that mapping
>> involves, necessarily, PVALID --> PVALID characters in
>> this case.
> Maybe there's something wrong with the definition of PVALID? If the
> initial PVALID-but-not-NFC character has to be mapped, because the
> strings must all be "in NFC form", then it's hard to understand how
> such a character is in fact valid under the protocol.
> (To be clear, I'm not complaining about what you're saying. You've
> made much more pointed the sort of thing that was nagging at me
> earlier today.)
#-# Martin J. Dürst, Professor, Aoyama Gakuin University
#-# http://www.sw.it.aoyama.ac.jp mailto:duerst at it.aoyama.ac.jp
More information about the Idna-update