Lower casing

Simon Josefsson simon at josefsson.org
Thu Jan 27 22:21:58 CET 2011

John C Klensin <klensin at jck.com> writes:

>>> 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.

Thank you for confirmation.  This resolves another ambiguity I had when
implementing this aspect.


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