Lower casing

[Mark Davis ☕]

2011/1/27 John C Klensin <klensin at jck.com>

>
>
> --On Thursday, January 27, 2011 08:56 -0800 Mark Davis ☕
> <mark at macchiato.com> wrote:
>
> > Mark
> >...
> >> > The B lines are valid for both T and N, so you should
> >> > include them.
> >>
> >> Then I'm stuck, and I would appreciate clarification from
> >> everyone about what IDNA2008 is saying.  Your second test
> >> case is:
> >>
> >> B;      FASS.DE;        fass.de;        ;
> >>
> >> The only place (that I can find) where IDNA2008 converts to
> >> lower case is in the following paragraph:
> >...
> > Sorry I wasn't not clear; The second column is the "Source",
> > which you need to ignore since you are not mapping.
> >
> > Let's take a couple of lines:
> >
> > N;    Faß.de; faß.de <http://fass.de> <http://fass.de>;
> xn--fa-hia.de;
> >
> > You would only look at the 3rd and 4th columns for testing, so
> > faß.de <http://fass.de><http://fass.de>
> > and xn--fa-hia.de.
> >...
>
> Mark, as a suggestion for both the tool and the web page, it may
> be worth noting that, while mapping (or one flavor or another)
> is optional with IDNA2008, the one restriction is that one must
> not map a PVALID character to something else.  Whatever the
> advantages of doing so --for transition reasons, personal
> preferences, or otherwise-- a program or system that remaps one
> PVALID character into one or more others is not in conformance
> with the intent of the IDNA2008 standards.
>

Yes, I agree.

The only 4 characters that have such a mapping are for the transitional
(migration) from IDNA2003. It should be clear from the text that such a
mapping isn't fully conformant to IDNA2008; if it needs further
clarification, let me know.

In adding instructions for IDNA2008 testing, we'll make it clear that the T
lines should be skipped for fully IDNA2008 conformant implementations.



> >...
> > The other take-away I have from this is that we need to have
> > clearer instructions for those who want to use the file, and
> > that do not support mapping. I'll add that to a list of
> > feedback for the committee.
>
> Please.
>
>
> >...
> >> However "FASS.DE" is not an A-label.
> >>
> >> Is there anything else in IDNA2008 that lower case labels?
>
> There is nothing at all in IDNA2008 that lower-cases labels,
> much less applying the Unicode case folding operation (which is
> quite controversial, especially as a character-replacement
> mapping algorithm).
>
> >> Further, I don't interpret the above to cause case conversion
> >> of the string looked up in DNS.  I only interprete it as
> >> converting it to lower case for the purpose of comparing with
> >> the output from the Punycode output.  It would be nice if
> >> someone could confirm or reject this interpretation as well.
>
> That interpretation is correct.  Note also that conversion of
> "ß" (U+00DF/  Sharp S/ Eszett) to "ss" is not a lower case
> conversion operation (because U+00DF is already lower case.  It
> results from a case-folding operation instead.
>
> best regards,
>    john
>
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