On Thursday, January 12, 2017 10:35:11 AM CET Daniel Stenberg wrote:
> On Wed, 11 Jan 2017, Tim Ruehsen wrote:
> > The IDN2_TRANSITIONAL enables TR46 'transitional' conversion (tries to be
> > compatible to IDNA2008 and IDNA2003 as much as possible),
> > IDN2_NONTRANSITIONAL enables TR46 'non-transitional (IDNA2008, the way
> > that
> > every app should go... may arise some incompatibilties with IDNA2003 which
> > is still under heavy use).
>
> Can you elaborate on some specific incompatibilties you're aware of? Aren't
> the problem mostly that there are still clients using IDNA2003 and not so
> much in the other end?

I just can tell you "rumors" that I heard/read.
- Some registries still use IDNA2003 (unsure, read it on Twitter a while ago)
- IDNs in TLS certificates are still encoded with IDNA2003 (likely)

Nikos Mavrogiannopoulos on help-libidn_at_gnu.org (3. Jan 2017)
"The thing is that RFC5280 references the IDNA2003 RFC, though this has
been obsoleted by IDNA2008 (RFC). Thus one can assume that the latter
is to be supported now (though details on whether TR#46 is to be used
are left as an exercise to the reader)."

There is a FAQ from Unicode which answers lot's of questions:
http://unicode.org/faq/idn.html

Tim

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