Lower casing

[John C Klensin]

--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>;	xn--fa-hia.de;	
> 
> You would only look at the 3rd and 4th columns for testing, so
> 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.

>...
> 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