Re: Combining characters (was: Re: [idn] hostname historyhell)

[David Hopwood <david.hopwood@zetnet.co.uk>]

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David Hopwood wrote:
> Soobok Lee wrote:
> > Now that <I><dot-above> is downcased to <i> as an exceptional case,
> > Then, we have an interesting question:
> > which direction should we  lowercase   <I><dot-above><acute>   into ?
> 
> To <i acute>. That is, the equivalence class is:
> 
>   <I><dot-above><acute>                         U+0049 U+0307 U+0301
>   <I dot-above><acute>                          U+0130 U+0301
>   <I><acute>                                    U+0049 U+0301
>   <I acute>                                     U+00CD
>   <i><acute>                                    U+0069 U+0301
>   <i acute>                                     U+00ED
>   <dotless i><acute>                            U+0131 U+0301
>   <fullwidth I><acute>                          U+FF29 U+0301
>   <fullwidth I><dot-above><acute>               U+FF29 U+0307 U+0301
>   <fullwidth i><acute>                          U+FF49 U+0301
> 
> and if NFKC is used, also: [snip]
> 
> <i acute> U+00ED is the normalised representative for all of these.
> 
> <i><dot-above><acute> is in a different equivalence class (AFAIK, no
> language uses it, so this doesn't matter).

My mistake; it is used in Lithuanian. The Lithuanian usage would argue
for <i><dot-above><acute> being in the same equivalence class (since its
Lithuanian uppercase form is <I acute>). So, another solution that
should be considered is to use NFC o fold as in the current version of
stringprep, but map out U+0307 whenever it is attached to a character
based on 'i' or 'I'. That wouldn't cause any problems for Turkish or
Azeri. I'll list all the options in another post.

- -- 
David Hopwood <david.hopwood@zetnet.co.uk>

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