There are two set of rules, one for non-Turkish

# Preserve canonical equivalence for I with dot. Turkic is handled below.

0130; 0069 0307; 0130; 0130; # LATIN CAPITAL LETTER I WITH DOT ABOVE

And another for Turkish

# Turkish and Azeri
 
# I and i-dotless; I-dot and i are case pairs in Turkish and Azeri
# The following rules handle those cases.
 
0130; 0069; 0130; 0130; tr; # LATIN CAPITAL LETTER I WITH DOT ABOVE
0130; 0069; 0130; 0130; az; # LATIN CAPITAL LETTER I WITH DOT ABOVE
 
# When lowercasing, remove dot_above in the sequence I + dot_above, which will turn into i.
# This matches the behavior of the canonically equivalent I-dot_above
 
0307; ; 0307; 0307; tr After_I; # COMBINING DOT ABOVE
0307; ; 0307; 0307; az After_I; # COMBINING DOT ABOVE
 
# When lowercasing, unless an I is before a dot_above, it turns into a dotless i.
 
0049; 0131; 0049; 0049; tr Not_Before_Dot; # LATIN CAPITAL LETTER I
0049; 0131; 0049; 0049; az Not_Before_Dot; # LATIN CAPITAL LETTER I
 
# When uppercasing, i turns into a dotted capital I
 
0069; 0069; 0130; 0130; tr; # LATIN SMALL LETTER I
0069; 0069; 0130; 0130; az; # LATIN SMALL LETTER I
 
# Note: the following case is already in the UnicodeData.txt file.
 
# 0131; 0131; 0049; 0049; tr; # LATIN SMALL LETTER DOTLESS I

If I understand this correctly, when we test the IDNA behavior of the uppercase string in a Turkish setting we should see the behavior described in the second part.

-Dennis

From: Latingp <latingp-bounces@icann.org> on behalf of Mats Dufberg <mats.dufberg@internetstiftelsen.se>
Date: Thursday, May 14, 2020 at 4:27 PM
To: ICANN Latin GP <Latingp@icann.org>
Subject: [EXTERNAL] [Latingp] Handling of down casing of I-dotted in Turkish locale

The link below goes to the file in the Unicode database that handles the special casing rules for i etc in Turkish and Azerian (sp?). The relevant section is the last section of the file.

https://unicode.org/Public/UNIDATA/SpecialCasing.txt

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Mats Dufberg

mats.dufberg@internetstiftelsen.se

Technical Expert

Internetstiftelsen (The Swedish Internet Foundation)

Mobile: +46 73 065 3899

https://internetstiftelsen.se/