At least the three following tests are failing a new assertion added with https://commits.webkit.org/258991@main fast/css/variables/env/invalid-env-name-fallback.html fast/css/variables/test-suite/166.html imported/w3c/web-platform-tests/css/css-variables/variable-declaration-29.html ASSERTION FAILED: isCustomPropertyName(name) style/CustomPropertyRegistry.cpp(45) : const WebCore::CSSRegisteredCustomProperty *WebCore::Style::CustomPropertyRegistry::get(const WTF::AtomString &) const 1 0x144053de4 WTFCrash 2 0x105fa4790 WTFCrashWithInfo(int, char const*, char const*, int) 3 0x10b398ae8 WebCore::Style::CustomPropertyRegistry::get(WTF::AtomString const&) const 4 0x108d98854 WebCore::CSSVariableReferenceValue::resolveVariableFallback(WTF::AtomString const&, WebCore::CSSParserTokenRange, WebCore::Style::BuilderState&) const 5 0x108d98dc0 WebCore::CSSVariableReferenceValue::resolveVariableReference(WebCore::CSSParserTokenRange, WebCore::CSSValueID, WTF::Vector<WebCore::CSSParserToken, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, WebCore::Style::BuilderState&) const 6 0x108d98ad0 WebCore::CSSVariableReferenceValue::resolveTokenRange(WebCore::CSSParserTokenRange, WebCore::Style::BuilderState&) const 7 0x108d99330 WebCore::CSSVariableReferenceValue::resolveVariableReferences(WebCore::Style::BuilderState&) const 8 0x108ed5668 WebCore::CSSParser::parseValueWithVariableReferences(WebCore::CSSPropertyID, WebCore::CSSValue const&, WebCore::Style::BuilderState&) 9 0x10b3ef9c0 WebCore::Style::Builder::resolveVariableReferences(WebCore::CSSPropertyID, WebCore::CSSValue&) 10 0x10b3ef04c WebCore::Style::Builder::applyProperty(WebCore::CSSPropertyID, WebCore::CSSValue&, WebCore::SelectorChecker::LinkMatchMask) 11 0x10b40be54 WebCore::Style::Builder::applyCascadeProperty(WebCore::Style::PropertyCascade::Property const&)::'lambda'(WebCore::SelectorChecker::LinkMatchMask)::operator()(WebCore::SelectorChecker::LinkMatchMask) const 12 0x10b3ee5e4 WebCore::Style::Builder::applyCascadeProperty(WebCore::Style::PropertyCascade::Property const&) 13 0x10b3ee404 WebCore::Style::Builder::applyDeferredProperties() 14 0x10b3ee288 WebCore::Style::Builder::applyNonHighPriorityProperties() 15 0x10b44653c WebCore::Style::Resolver::applyMatchedProperties(WebCore::Style::Resolver::State&, WebCore::Style::MatchResult const&) 16 0x10b444b18 WebCore::Style::Resolver::styleForElement(WebCore::Element const&, WebCore::Style::ResolutionContext const&, WebCore::RuleMatchingBehavior) 17 0x10b453dcc WebCore::Style::TreeResolver::styleForStyleable(WebCore::Styleable const&, WebCore::Style::TreeResolver::ResolutionType, WebCore::Style::ResolutionContext const&) 18 0x10b454348 WebCore::Style::TreeResolver::resolveElement(WebCore::Element&, WebCore::RenderStyle const*, WebCore::Style::TreeResolver::ResolutionType) 19 0x10b4577d8 WebCore::Style::TreeResolver::resolveComposedTree() 20 0x10b458a4c WebCore::Style::TreeResolver::resolve() 21 0x1091f6b90 WebCore::Document::resolveStyle(WebCore::Document::ResolveStyleType) 22 0x1091f7a78 WebCore::Document::updateStyleIfNeeded() 23 0x109213cb0 WebCore::Document::finishedParsing() 24 0x109a6b574 WebCore::HTMLConstructionSite::finishedParsing() 25 0x109ab3bb8 WebCore::HTMLTreeBuilder::finished() 26 0x109a7383c WebCore::HTMLDocumentParser::end() 27 0x109a71778 WebCore::HTMLDocumentParser::attemptToRunDeferredScriptsAndEnd() 28 0x109a714d0 WebCore::HTMLDocumentParser::prepareToStopParsing() 29 0x109a738a8 WebCore::HTMLDocumentParser::attemptToEnd() 30 0x109a73978 WebCore::HTMLDocumentParser::finish() 31 0x109f502e4 WebCore::DocumentWriter::end() https://results.webkit.org/?suite=layout-tests&suite=layout-tests&suite=layout-tests&test=fast%2Fcss%2Fvariables%2Fenv%2Finvalid-env-name-fallback.html&test=fast%2Fcss%2Fvariables%2Ftest-suite%2F166.html&test=imported%2Fw3c%2Fweb-platform-tests%2Fcss%2Fcss-variables%2Fvariable-declaration-29.html