plea for NFKC & case-folding, suggestions for definitions

Mark Davis mark at macchiato.com
Tue Mar 3 18:02:56 CET 2009


There is already a draft mapping on http://unicode.org/reports/tr46/ -
feedback is welcome.

Mark


On Mon, Mar 2, 2009 at 22:28, Adam M. Costello
<idna-update.amc+0+ at nicemice.net.removethisword> wrote:

> Harald Alvestrand <harald at alvestrand.no> wrote:
>
> > do you think that the canonicalization function you're positing can be
> > described in an Unicode-version-independent way?
>
> I think it can, but I'll need help from our resident Unicode experts to
> provide the definition.
>
> The Unicode standard promises normalization stability from
> version 4.1 onward, and case-folding stability from version
> 5.0 onward.  Section 3.13 of version 5.0 suggests this for
> compatibility-normalize-and-case-fold:
>
>     NFKD(toCasefold(NFKD(toCasefold(NFD(X))))) =
>
> I don't know why so many iterations are needed, and I don't know why the
> first step is NFD rather than NFKD.
>
> We would of course want to change the last NFKD (or both of them) to
> NFKC.
>
> After applying this function, we would then check the result for
> disallowed code points and other violations (described in the existing
> drafts), and either return it or return an error.
>
> We'd have to consider & specify what to do about the handful of obscure
> incompatibilites between Unicode 3.2 and 5.0, but we should never have
> to do that again because of the newer Unicode stability policies.
>
> Unicode experts, please comment on the feasibility of this approach, and
> suggest ways to simplify it if you can think of any.
>
> Thanks,
> AMC
> - Show quoted text -
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