Re: Case mapping of sharp s

[Eli Zaretskii <eliz@gnu.org>]

> From: Kenichi Handa <handa@m17n.org>
> Date: Mon, 16 Nov 2009 21:06:38 +0900
> Cc: emacs-devel@gnu.org
> 
> In article <19200.4158.380820.761685@a1i15.kph.uni-mainz.de>, Ulrich Mueller <ulm@gentoo.org> writes:
> 
> > In Unicode since version 5.1.0 the U+1E9E code point is assigned to
> > "LATIN CAPITAL LETTER SHARP S". Would it be possible to add a mapping
> > from this to the lower case ß, as in the patch below?
> 
> > However, I've noticed that similar mappings for Turkish ı (dotless i)
> > and İ (I with dot) were commented out [1]. Is it still so that such a
> > change would "make searches slow", as stated in the comment?
> 
> That kind of setting surely makes the searching of ß and ẞ
> slow because we can't use BM search when case-fold-search is
> non-nil.  BM search is possible only when all
> case-equivalent characters are represented by the same byte
> length, and differ only in the last byte.

I think we need to solve this limitation anyway, if we want a decent
support for Unicode.  There are many more pairs of characters that
should normally be considered equal in search.

Wouldn't the technique described in UTS 18
(http://www.unicode.org/reports/tr18/) help here?