Bug 256716 – DOMXPath- failing (fn-lang.html) due to U+212A handling

• Status: NEW
• Component: XML

[Ahmad Saleem]

Hi Team,

While going through WPT test cases, came across one sub-test failure:

Test Case - https://wpt.fyi/results/domxpath/fn-lang.html?label=experimental&label=master&aligned

Link - http://wpt.live/domxpath/fn-lang.html

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Researching bit on when this was added and against which bugs, it seems to be U+212A handling issue either in CSS or DOM level.

Just raising, so we can fix it.

Thanks!

[Alexey Proskuryakov]

// U+212A should match to ASCII 'k'.
// XPath 1.0 says:
// ... such that the attribute value is equal to the argument ignoring that suffix
// of the attribute value and ignoring case.
// XPath 3.1 says:
// ... true if and only if, based on a caseless default match as specified in
// section 3.13 of The Unicode Standard,
testFirstChild('lang("ko")', '<root><match xml:lang="&#x212A;o"/></root>');

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So this test says that U+212A KELVIN SIGN should match letter "k" in lang attribute, which seems weird, at least initially.

The Unicode Standard reference here is obsolete, but is almost certainly about "caseless matching" in https://www.unicode.org/versions/Unicode15.0.0/ch05.pdf. Which indeed has this behavior, but the rest of the Web platform does not AFAIK. Notably, even Chrome doesn't have this behavior for CSS selector matching.

I think that this is a bug in the standard, and Chrome is internally inconsistent, so we shouldn't be following it. CC'ing some folks who've done more recent work in this area to weigh in.

[Alexey Proskuryakov]

Created attachment 466349 [details]
CSS selector test

[Anne van Kesteren]

Looking at the source of the test it seems this was done based on an XPath 3.1 clarification, but indeed we use ASCII case-insensitive for language matching across the web platform. Let's change this test and add a clarification to DOM/HTML with regards to what kind of matching the XPath lang() function uses.

[Radar WebKit Bug Importer]

<rdar://problem/109571692>

[Ahmad Saleem]

Modifying the test upstream in WPT - https://github.com/web-platform-tests/wpt/pull/45436