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Re: case-insensitive string comparison

From: Roland Winkler
Subject: Re: case-insensitive string comparison
Date: Wed, 20 Jul 2022 13:10:35 -0500

On Wed, Jul 20 2022, Eli Zaretskii wrote:
>> Even mentioning the difficulties could be useful here.
> I'm not sure I agree.  To describe all the important aspects of this
> would take too long, and it isn't the job of our manual to document
> this stuff.  Read this if you want to know:
>   https://unicode.org/reports/tr10/

A footnote pointing the interested reader to this report could already
be useful.  I am not suggesting to try to provide a more exhaustive
discussion of this topic.  I am suggesting to mention briefly that the
topic is subtle and depends on details "beyond emacs itself".

>> I am not sure I can follow your argument.  Do you suggest that, likely,
>> BBDB will work best if it compares names using compare-strings?
> Yes.

Thanks, that's already good to know!

> But in addition, you should set up the case table of the current
> buffer when you do so, because otherwise special cases with the likes
> of the Turkish language's dotless I could in rare cases screw you.
>> (I'd be glad to hear that.)  This code should work for users who do not
>> want to build their own case table and stuff like that.
> Not the users should build the case table, BBDB (or whatever Lisp
> program that needs the comparison) should.  It's not that hard,
> really: if you only need ASCII, use ascii-case-table, otherwise copy
> the standard case-table and modify it to make sure I downcases to i
> and similarly with a few other exceptional letters.

I am not sure it would be possible to predict how a default case table
for BBDB should differ from the standard case table.  BBDB might be the
only package of a user that accumulates strings that go beyond what
otherwise a user is dealing with regularly.  If there is a sensible
"BBDB default case table" I'd hope that this is the standard case table.

Or if not: can you suggest an emacs package that I can look into as a
source of inspiration?

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