Dear <oXygen/> support, I'm trying to case-fold some early Cyrillic text, which includes characters from the Unicode Cyrillic B range ( http://www.unicode.org/charts/PDF/UA640.pdf), and the lower-case() function does not seem to be returning what I expect. I am testing in the XPath browser box in <oXygen/> 14.1 (set to XPath 2.0), but I get the same results when performing an XSLT transformation using Saxon-PE 9.4.0.4. Input: string-to-codepoints('Ꙗ') Output (as expected): 42582 Input: string-to-codepoints(lower-case('Ꙗ')) Output (incorrect): 42582 That is, I get the same result when I process this upper-case letter regardless of whether I try to convert it to lower case. The lower-case counterpart of U+A656 is U+A657. The case mapping seems to be correct in the Unicode property table at http://www.unicode.org/Public/UNIDATA/UnicodeData.txt, where the relevant lines are: A656;CYRILLIC CAPITAL LETTER IOTIFIED A;Lu;0;L;;;;;N;;;;A657; A657;CYRILLIC SMALL LETTER IOTIFIED A;Ll;0;L;;;;;N;;;A656;;A656 For comparison (ASCII-range characters): Input: string-to-codepoints('A') Output (as expected): 65 Input: string-to-codepoints(lower-case('A')) Output (as expected): 97 It looks, then, as if the lower-case() function works properly on some Unicode characters, such as those in the ASCII range, but not on others, such as those in the Cyrillic B range. The Cyrillic B characters have been in Unicode since version 5.1.0 (April 4, 2008); Unicode is now at 6.2.0. Is this a bug (and if so, whose bug is it?), or are my expectations based on a misunderstanding? Thanks, David (djbpitt@gmail.com)