Re: [I18nrp] Mappings for IDNA2008 ?

Andrew Sullivan <> Fri, 08 February 2019 19:55 UTC

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From: Andrew Sullivan <>
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Subject: Re: [I18nrp] Mappings for IDNA2008 ?
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On Fri, Feb 08, 2019 at 08:47:24PM +0100, Patrik Fältström wrote:
> For example, if I as a user with $LC_CTYPE == sv_SE.UTF-8 do type or view a string of characters, then I am pretty sure I am interested in having case folding and others things mapped according to that LOCALE. But only when/if the input/output should include such mappings. Most of them should probably not have any mappings at all.

Yes.  And the way to mess with you is to (e.g.) send you something
that has various foldings or mappings in _your_ locale that are not
the same as the various foldings and mappings in the locale with which
the string was generated.  These are blessedly rare, but they're not
"never", which is John's point upthread about working irregularly vs
working.  This gets even worse when the mappings vary according to
application or whatever, which is _also_ a potential feature of IDNA.

UTS#46 doesn't do anything to help this _either_ because it is no more
able to know the locale-at-identifier-generation time than anything
else is, because that information is simply not carried around with
the identifier.

This problem is, I should note, well understood among network protocol
people, who spent a lot of time talking about it during PRECIS.  But
it keeps coming back up because people keep forgetting that these
protocols are locale-free even if you think you know the locale at
lookup time.


Andrew Sullivan