Attachment 480532 Details for Bug 319178 – Patch

[patch] Patch

bug-319178-20260712052550.patch (text/plain), 101.02 KB, created by alan on 2026-07-12 05:25:51 PDT

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Creator: alan

Created: 2026-07-12 05:25:51 PDT

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patch

obsolete

>From 6eb89e5ba9e9a5dfb00b3d1ba169affdd4b9ca7c Mon Sep 17 00:00:00 2001
>From: Alan Baradlay <zalan@apple.com>
>Date: Sat, 11 Jul 2026 20:20:13 -0700
>Subject: [PATCH] [css-text-decor-4] Implement the text-decoration-inset
> property https://bugs.webkit.org/show_bug.cgi?id=319178
> <rdar://problem/182019037>
>
>Reviewed by NOBODY (OOPS!).
>
>Add the CSS Text Decoration Level 4 'text-decoration-inset' property
>(auto | <length>{1,2}), gated behind the cssTextDecorationInsetEnabled setting.
>
>The property adjusts the start and end endpoints of the line decorations drawn by
>a decorating box (underline, overline, line-through). A positive <length> moves
>an endpoint inward, trimming the decoration; a negative <length> moves it outward,
>extending it. A single value applies to both endpoints; two values are the start
>and the end. 'auto' lets the UA choose an inset so that two adjacent identical
>underlined elements do not appear to share a single continuous underline (e.g.
>for Chinese, where underlining is a form of punctuation); it is distinct from 0.
>
>1. It is stored as a new Style::TextDecorationInset value type (a keyword-or-length-
>pair) in NonInheritedRareData, parsed grammar-driven, and animated by computed
>value.
>2. The inset is applied at paint time in TextBoxPainter, which shifts the
>decoration's inline origin and shrinks/grows its length (because text-decoration-
>inset and box-decoration-break are not inherited, a decoration that propagates
>from an ancestor box down to the (root inline) box that paints it)
>3. box-decoration-break is then honored via the inline box's closed edges: with 'slice' the start
>inset only affects the first fragment's start edge and the end inset the last
>fragment's end edge; with 'clone' both edges of every fragment are inset.
>4. Endpoints are also gated on the marked-text piece that actually reaches the box's
>logical start/end, so a decoration split into several marked texts (selection,
>document markers, highlights) stays continuous instead of being trimmed at the
>interior boundaries.
>5. Because a negative inset extends the decoration past the text
>box, decoration ink overflow is expanded by the outward amount, and StyleDifference
>treats an inset change as affecting repaint and visual overflow so dynamic/animated
>changes invalidate correctly.
>
>Horizontal and vertical writing modes (including sideways-rl/lr and orthogonal
>blocks), in both inline directions, are supported, as is the text-decoration-skip-
>ink interaction (its skip gaps are measured against the underline's bounding box,
>which already tracks the inset-shifted origin, so they stay aligned to the glyphs).
>Across a bidi direction boundary the decoration is painted one segment per run; the
>component of the inset that shifts the decoration as a whole is applied to every
>segment (so the seam between runs moves with it rather than being pinned), while the
>extend/trim overhang is applied only at the segment reaching the decoration's visual
>start/end.
>
>* LayoutTests/TestExpectations: Un-skip the now-passing upstream WPT conformance
>tests (text-decoration-inset-001..008, 010..013, 015..024, and
>orthogonal-block-001); 009/014 (sub-pixel endpoint rounding) and the unrelated 025
>(multicol) remain ImageOnlyFailure on follow-up bugs.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-cascade/all-prop-initial-xml-expected.txt:
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-computed-expected.txt:
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-valid-expected.txt: Rebaseline the upstream parsing tests, which still carried the pre-implementation "not supported" baseline.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-expected-mismatch.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break-expected-mismatch.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed-expected.txt: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid-expected.txt: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative-expected-mismatch.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-ref.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid-expected.txt: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero-expected.html: Added.
>* LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero.html: Added.
>* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml: Add CSSTextDecorationInsetEnabled.
>* Source/WebCore/Headers.cmake:
>* Source/WebCore/Sources.txt:
>* Source/WebCore/WebCore.xcodeproj/project.pbxproj: Build StyleTextDecorationInset.
>* Source/WebCore/css/CSSProperties.json: Add the text-decoration-inset property.
>* Source/WebCore/rendering/TextBoxPainter.cpp:
>(WebCore::autoTextDecorationInset):
>(WebCore::TextBoxPainter::insetAdjustedDecorationLocationAndWidth): Apply the
>inset (and box-decoration-break) carried on the decoration styles to the decoration
>geometry, honoring box-decoration-break and marked-text sub-ranges.
>(WebCore::TextBoxPainter::paintBackgroundDecorations):
>(WebCore::TextBoxPainter::paintForegroundDecorations):
>(WebCore::TextBoxPainter::insetAdjustedDecorationLocationAndWidth const):
>* Source/WebCore/rendering/TextBoxPainter.h:
>* Source/WebCore/rendering/TextDecorationPainter.cpp:
>(WebCore::collectStylesForRenderer): Also resolve the non-inherited
>text-decoration-inset and box-decoration-break from the box that introduces the
>decoration, alongside its color/thickness/style.
>(WebCore::TextDecorationPainter::Styles::operator==):
>(WebCore::TextDecorationPainter::Styles::operator== const):
>* Source/WebCore/rendering/TextDecorationPainter.h: Carry the resolved inset and
>box-decoration-break on Styles.
>* Source/WebCore/style/InlineTextBoxStyle.cpp:
>(WebCore::computedInkOverflowForDecorations): Expand ink overflow for a negative
>(outward) inset.
>* Source/WebCore/style/PropertyAllowlist.cpp: Allow text-decoration-inset in the
>(WebCore::Style::isValidHighlightStyleProperty):
>(WebCore::Style::isValidCueStyleProperty):
>(WebCore::Style::isValidCueSelectorStyleProperty):
>highlight and cue property allowlists.
>* Source/WebCore/style/StyleBuilderCustom.h: Add forwardInheritedValue overload.
>(WebCore::Style::forwardInheritedValue):
>* Source/WebCore/style/StyleDifference.cpp:
>(WebCore::...::changeAffectsVisualOverflow):
>(WebCore::...::rareDataChangeRequiresRepaint): Repaint/recompute overflow when
>the inset changes.
>* Source/WebCore/style/computed/data/StyleNonInheritedRareData.cpp:
>(WebCore::Style::NonInheritedRareData::NonInheritedRareData):
>(WebCore::Style::NonInheritedRareData::operator== const):
>(WebCore::Style::NonInheritedRareData::dumpDifferences const):
>* Source/WebCore/style/computed/data/StyleNonInheritedRareData.h: Store the inset.
>* Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.cpp: Added.
>(WebCore::Style::TextDecorationInset::resolvedStart const):
>(WebCore::Style::TextDecorationInset::resolvedEnd const):
>(WebCore::Style::CSSValueConversion<TextDecorationInsetPair>::operator):
>* Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.h: Added.
>(WTF::MarkableTraits<WebCore::Style::TextDecorationInsetPair>::isEmptyValue):
>(WTF::MarkableTraits<WebCore::Style::TextDecorationInsetPair>::emptyValue):
>(WebCore::Style::TextDecorationInset::TextDecorationInset):
>(WebCore::Style::TextDecorationInset::isAuto const):
>* Source/WebCore/style/computed/StyleComputedStyleBase.h:
>* LayoutTests/imported/w3c/web-platform-tests/html/rendering/widgets/shadow-dom-expected.txt:
>---
> .../Preferences/UnifiedWebPreferences.yaml    | 15 +++
> Source/WebCore/Headers.cmake                  |  1 +
> Source/WebCore/Sources.txt                    |  1 +
> .../WebCore/WebCore.xcodeproj/project.pbxproj |  6 ++
> Source/WebCore/css/CSSProperties.json         | 18 ++++
> Source/WebCore/rendering/TextBoxPainter.cpp   | 96 ++++++++++++++++++-
> Source/WebCore/rendering/TextBoxPainter.h     |  7 ++
> .../rendering/TextDecorationPainter.cpp       |  9 +-
> .../WebCore/rendering/TextDecorationPainter.h |  4 +
> Source/WebCore/style/InlineTextBoxStyle.cpp   | 13 +++
> Source/WebCore/style/PropertyAllowlist.cpp    |  3 +
> Source/WebCore/style/StyleBuilderCustom.h     |  1 +
> Source/WebCore/style/StyleDifference.cpp      |  5 +-
> .../style/computed/StyleComputedStyleBase.h   |  1 +
> .../data/StyleNonInheritedRareData.cpp        |  4 +
> .../computed/data/StyleNonInheritedRareData.h |  2 +
> .../StyleTextDecorationInset.cpp              | 75 +++++++++++++++
> .../StyleTextDecorationInset.h                | 84 ++++++++++++++++
> LayoutTests/TestExpectations                  | 33 ++-----
> .../all-prop-initial-xml-expected.txt         |  1 +
> ...ext-decoration-inset-computed-expected.txt | 20 ++--
> .../text-decoration-inset-valid-expected.txt  | 20 ++--
> ...xt-decoration-inset-auto-cjk-expected.html | 11 +++
> .../text-decoration-inset-auto-cjk.html       | 12 +++
> ...coration-inset-auto-expected-mismatch.html |  5 +
> .../text-decoration-inset-auto.html           |  7 ++
> ...ox-decoration-break-expected-mismatch.html |  9 ++
> ...decoration-inset-box-decoration-break.html | 11 +++
> ...ext-decoration-inset-computed-expected.txt | 20 ++++
> .../text-decoration-inset-computed.html       | 96 +++++++++++++++++++
> ...text-decoration-inset-invalid-expected.txt | 17 ++++
> .../text-decoration-inset-invalid.html        | 35 +++++++
> ...ecoration-inset-line-through-expected.html |  5 +
> .../text-decoration-inset-line-through.html   |  7 ++
> ...ration-inset-marked-text-gap-expected.html | 12 +++
> ...text-decoration-inset-marked-text-gap.html | 24 +++++
> ...tion-inset-negative-expected-mismatch.html |  5 +
> .../text-decoration-inset-negative.html       |  7 ++
> ...coration-inset-not-inherited-expected.html |  5 +
> .../text-decoration-inset-not-inherited.html  |  7 ++
> ...t-decoration-inset-one-value-expected.html |  5 +
> .../text-decoration-inset-one-value.html      |  7 ++
> ...xt-decoration-inset-overline-expected.html |  5 +
> .../text-decoration-inset-overline.html       |  7 ++
> ...ration-inset-trims-underline-expected.html |  8 ++
> ...-decoration-inset-trims-underline-ref.html |  8 ++
> ...text-decoration-inset-trims-underline.html | 12 +++
> .../text-decoration-inset-valid-expected.txt  | 24 +++++
> .../text-decoration-inset-valid.html          | 40 ++++++++
> .../text-decoration-inset-zero-expected.html  |  5 +
> .../text-decoration-inset-zero.html           |  7 ++
> .../rendering/widgets/shadow-dom-expected.txt |  8 +-
> 52 files changed, 794 insertions(+), 56 deletions(-)
> create mode 100644 Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.cpp
> create mode 100644 Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.h
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-expected-mismatch.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break-expected-mismatch.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed-expected.txt
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid-expected.txt
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative-expected-mismatch.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-ref.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid-expected.txt
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero-expected.html
> create mode 100644 LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero.html
>
>diff --git a/Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml b/Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml
>index 7e49e29ae834..3baa22b94a7d 100644
>--- a/Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml
>+++ b/Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml
>@@ -1541,6 +1541,21 @@ CSSSelectorJITCompilerEnabled:
>     WebCore:
>       default: true
> 
>+CSSTextDecorationInsetEnabled:
>+  type: bool
>+  status: preview
>+  category: css
>+  webcoreOnChange: setNeedsRecalcStyleInAllFrames
>+  humanReadableName: "CSS text-decoration-inset property"
>+  humanReadableDescription: "Enable the text-decoration-inset property, defined in CSS Text Decoration 4"
>+  defaultValue:
>+    WebKitLegacy:
>+      default: false
>+    WebKit:
>+      default: false
>+    WebCore:
>+      default: false
>+
> CSSTextDecorationLineErrorValues:
>   type: bool
>   status: stable
>diff --git a/Source/WebCore/Headers.cmake b/Source/WebCore/Headers.cmake
>index a3a66cea6431..9b6925625ea5 100644
>--- a/Source/WebCore/Headers.cmake
>+++ b/Source/WebCore/Headers.cmake
>@@ -3498,6 +3498,7 @@ set(WebCore_PRIVATE_FRAMEWORK_HEADERS
>     style/values/text/StyleTextTransform.h
>     style/values/text/StyleWordSpacing.h
> 
>+    style/values/text-decoration/StyleTextDecorationInset.h
>     style/values/text-decoration/StyleTextDecorationLine.h
>     style/values/text-decoration/StyleTextDecorationThickness.h
>     style/values/text-decoration/StyleTextEmphasisPosition.h
>diff --git a/Source/WebCore/Sources.txt b/Source/WebCore/Sources.txt
>index 52a2e0bbb67a..b282150fbd99 100644
>--- a/Source/WebCore/Sources.txt
>+++ b/Source/WebCore/Sources.txt
>@@ -3491,6 +3491,7 @@ style/values/svg/StyleSVGPaintOrder.cpp
> style/values/svg/StyleSVGPathData.cpp
> style/values/svg/StyleSVGStrokeDasharray.cpp
> style/values/svg/StyleSVGStrokeDashoffset.cpp
>+style/values/text-decoration/StyleTextDecorationInset.cpp @header:RenderStyleGetters @cost:5
> style/values/text-decoration/StyleTextDecorationLine.cpp
> style/values/text-decoration/StyleTextDecorationThickness.cpp @header:RenderStyleGetters @cost:5
> style/values/text-decoration/StyleTextEmphasisPosition.cpp
>diff --git a/Source/WebCore/WebCore.xcodeproj/project.pbxproj b/Source/WebCore/WebCore.xcodeproj/project.pbxproj
>index ca4a387f00b7..dbd9c2d8e1fb 100644
>--- a/Source/WebCore/WebCore.xcodeproj/project.pbxproj
>+++ b/Source/WebCore/WebCore.xcodeproj/project.pbxproj
>@@ -734,6 +734,7 @@
> 		1C4DB02627339FE0007B0AD1 /* ShouldLocalizeAxisNames.h in Headers */ = {isa = PBXBuildFile; fileRef = 1C4DB02427339E5E007B0AD1 /* ShouldLocalizeAxisNames.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		1C5E1DA826F94B9000E07AF1 /* FontPaletteValues.h in Headers */ = {isa = PBXBuildFile; fileRef = 1C5E1DA626F949B900E07AF1 /* FontPaletteValues.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		1C6626111C6E7CA600AB527C /* FontFace.h in Headers */ = {isa = PBXBuildFile; fileRef = 1C66260F1C6E7CA600AB527C /* FontFace.h */; };
>+		1DEC0126000000000000A0DE /* StyleTextDecorationInset.h in Headers */ = {isa = PBXBuildFile; fileRef = 1DEC0126000000000000B0DE /* StyleTextDecorationInset.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		1C73A71521857587004CCEA5 /* StyleTextDecorationThickness.h in Headers */ = {isa = PBXBuildFile; fileRef = 1CB6B4F8217B83930093B9CD /* StyleTextDecorationThickness.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		1C7A6EB526F5D8F50096D8C7 /* FontPalette.h in Headers */ = {isa = PBXBuildFile; fileRef = 1C4674FD26F4843600B61273 /* FontPalette.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		1C81B95A0E97330800266E07 /* PageInspectorController.h in Headers */ = {isa = PBXBuildFile; fileRef = 1C81B9560E97330800266E07 /* PageInspectorController.h */; settings = {ATTRIBUTES = (Private, ); }; };
>@@ -9777,6 +9778,7 @@
> 		1CAF34800A6C405200ABE06E /* WebScriptObjectPrivate.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WebScriptObjectPrivate.h; sourceTree = "<group>"; };
> 		1CAF56D8253014570017B472 /* DrawGlyphsRecorder.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = DrawGlyphsRecorder.h; sourceTree = "<group>"; };
> 		1CAF56DE2530245A0017B472 /* DrawGlyphsRecorder.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = DrawGlyphsRecorder.cpp; sourceTree = "<group>"; };
>+		1DEC0126000000000000B0DE /* StyleTextDecorationInset.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = StyleTextDecorationInset.h; sourceTree = "<group>"; };
> 		1CB6B4F8217B83930093B9CD /* StyleTextDecorationThickness.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = StyleTextDecorationThickness.h; sourceTree = "<group>"; };
> 		1CC54AFB270F92DA005BF8BE /* ProcessQualified.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ProcessQualified.h; sourceTree = "<group>"; };
> 		1CCDF5BB1990332400BCEBAD /* SVGToOTFFontConversion.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SVGToOTFFontConversion.cpp; sourceTree = "<group>"; };
>@@ -19066,6 +19068,7 @@
> 		BC0929B02E2AA9BA002ACB2C /* StyleWebKitOverflowScrolling.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = StyleWebKitOverflowScrolling.cpp; sourceTree = "<group>"; };
> 		BC0929B12E2AA9BA002ACB2C /* StyleWebKitOverflowScrolling.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = StyleWebKitOverflowScrolling.h; sourceTree = "<group>"; };
> 		BC092A042E2D5110002ACB2C /* StyleCursor.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = StyleCursor.cpp; sourceTree = "<group>"; };
>+		1DEC0126000000000000C0DE /* StyleTextDecorationInset.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = StyleTextDecorationInset.cpp; sourceTree = "<group>"; };
> 		BC092A0C2E2D75E6002ACB2C /* StyleTextDecorationThickness.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = StyleTextDecorationThickness.cpp; sourceTree = "<group>"; };
> 		BC092A1B2E2DBC36002ACB2C /* StyleViewTransitionName.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = StyleViewTransitionName.cpp; sourceTree = "<group>"; };
> 		BC092A752E300E57002ACB2C /* StyleBlockStepSize.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = StyleBlockStepSize.h; sourceTree = "<group>"; };
>@@ -37827,6 +37830,8 @@
> 		BC3078E42D02884200630D75 /* text-decoration */ = {
> 			isa = PBXGroup;
> 			children = (
>+				1DEC0126000000000000C0DE /* StyleTextDecorationInset.cpp */,
>+				1DEC0126000000000000B0DE /* StyleTextDecorationInset.h */,
> 				4C1508782E512B4100B720D9 /* StyleTextDecorationLine.cpp */,
> 				4C1508772E512B4100B720D9 /* StyleTextDecorationLine.h */,
> 				BC092A0C2E2D75E6002ACB2C /* StyleTextDecorationThickness.cpp */,
>@@ -49129,6 +49134,7 @@
> 				BC452A922ED24DE500FD066C /* StyleTextAlignLast.h in Headers */,
> 				BC4631A32EAA911900EA911F /* StyleTextAutospace.h in Headers */,
> 				BC10DA912E80DC39000EE742 /* StyleTextBoxEdge.h in Headers */,
>+				1DEC0126000000000000A0DE /* StyleTextDecorationInset.h in Headers */,
> 				4C15087A2E512B4100B720D9 /* StyleTextDecorationLine.h in Headers */,
> 				1C73A71521857587004CCEA5 /* StyleTextDecorationThickness.h in Headers */,
> 				BC10DA8A2E80D200000EE742 /* StyleTextEdge.h in Headers */,
>diff --git a/Source/WebCore/css/CSSProperties.json b/Source/WebCore/css/CSSProperties.json
>index 2bd391f29ee5..421e35130aaa 100644
>--- a/Source/WebCore/css/CSSProperties.json
>+++ b/Source/WebCore/css/CSSProperties.json
>@@ -11903,6 +11903,24 @@
>                 "url": "https://drafts.csswg.org/css-text-decor-4/#text-decoration-thickness-property"
>             }
>         },
>+        "text-decoration-inset": {
>+            "animation-type": "by computed value",
>+            "initial": "0px",
>+            "values": [
>+                "auto"
>+            ],
>+            "codegen-properties": {
>+                "settings-flag": "cssTextDecorationInsetEnabled",
>+                "computed-style-storage-path": ["m_nonInheritedData", "rareData"],
>+                "computed-style-storage-kind": "reference",
>+                "computed-style-type": "Style::TextDecorationInset",
>+                "parser-grammar": "auto | <length>{1,2}@(type=CSSValuePair default=previous)"
>+            },
>+            "specification": {
>+                "category": "css-text-decor",
>+                "url": "https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property"
>+            }
>+        },
>         "-webkit-text-decorations-in-effect": {
>             "animation-type": "not animatable (internal)",
>             "inherited": true,
>diff --git a/Source/WebCore/rendering/TextBoxPainter.cpp b/Source/WebCore/rendering/TextBoxPainter.cpp
>index 61bc3f93d856..0769acd3ac91 100644
>--- a/Source/WebCore/rendering/TextBoxPainter.cpp
>+++ b/Source/WebCore/rendering/TextBoxPainter.cpp
>@@ -52,6 +52,7 @@
> #include "RenderView.h"
> #include "RenderedDocumentMarker.h"
> #include "Settings.h"
>+#include "StyleTextDecorationInset.h"
> #include "StyleTextDecorationLine.h"
> #include "StyleTextDecorationThickness.h"
> #include "StyledMarkedText.h"
>@@ -898,6 +899,91 @@ void TextBoxPainter::collectDecoratingBoxesForBackgroundPainting(DecoratingBoxLi
>     }
> }
> 
>+static float autoTextDecorationInset(const Style::ComputedStyle& style)
>+{
>+    // A small UA-chosen inset (relative to font size) so that two adjacent identical underlined
>+    // elements do not appear to share a single continuous underline (important for e.g. Chinese,
>+    // where underlining is a form of punctuation).
>+    return style.computedFontSize() / 8;
>+}
>+
>+std::pair<FloatPoint, float> TextBoxPainter::insetAdjustedDecorationLocationAndWidth(const DecoratingBox& decoratingBox, const StyledMarkedText& markedText) const
>+{
>+    auto boxOrigin = decoratingBox.location;
>+    auto width = decoratingBox.contentWidth;
>+
>+    // text-decoration-inset and box-decoration-break are not inherited, but a decoration propagates from
>+    // the box that introduces it to the (possibly descendant) box that paints it, so they are resolved
>+    // from the originating box and carried on the decoration Styles (see collectStylesForRenderer()),
>+    // alongside the decoration color/thickness.
>+    auto& insetStyles = decoratingBox.textDecorationStyles;
>+    if (!insetStyles.inset)
>+        return { boxOrigin, width };
>+    auto& inset = *insetStyles.inset;
>+
>+    auto& style = decoratingBox.style.get();
>+    auto autoValue = inset.isAuto() ? autoTextDecorationInset(style) : 0.f;
>+    auto startInset = inset.resolvedStart(style, autoValue);
>+    auto endInset = inset.resolvedEnd(style, autoValue);
>+    if (!startInset && !endInset)
>+        return { boxOrigin, width };
>+
>+    auto writingMode = style.writingMode();
>+    auto decoratingInlineBox = decoratingBox.inlineBox;
>+
>+    // box-decoration-break: the start inset applies only to the first fragment's start edge and the
>+    // end inset only to the last fragment's end edge; for box-decoration-break: clone every fragment is
>+    // a complete box, so both endpoints are inset on every line.
>+    auto closedEdges = [&]() -> RectEdges<bool> {
>+        if (!decoratingInlineBox)
>+            return { true };
>+        if (insetStyles.boxDecorationBreak == BoxDecorationBreak::Clone)
>+            return { true };
>+        return decoratingInlineBox->closedEdges();
>+    }();
>+
>+    bool isLTR = writingMode.isBidiLTR();
>+
>+    // A decorating box can span several leaf boxes on a line (its bidi runs), each split into marked-text
>+    // sub-ranges. Map the logical start/end insets onto the decoration's visual left/right edges;
>+    // displacements below are measured rightward (a positive inset trims inward, a negative one extends
>+    // outward). box-decoration-break decides which of the decoration's edges live on this line fragment,
>+    // and firstLeafBox/lastLeafBox + the marked-text offsets decide which painted piece actually reaches
>+    // that visual edge.
>+    auto textBox = makeIterator();
>+    bool ownsLineLeftEdge = !decoratingInlineBox || textBox == decoratingInlineBox->firstLeafBox();
>+    bool ownsLineRightEdge = !decoratingInlineBox || textBox == decoratingInlineBox->lastLeafBox();
>+    bool ownsLogicalStart = !markedText.startOffset;
>+    bool ownsLogicalEnd = markedText.endOffset == m_paintTextRun.length();
>+
>+    float visualLeftInset = isLTR ? startInset : endInset;
>+    float visualRightInset = isLTR ? endInset : startInset;
>+    bool leftEdgeOnFragment = isLTR ? closedEdges.start(writingMode) : closedEdges.end(writingMode);
>+    bool rightEdgeOnFragment = isLTR ? closedEdges.end(writingMode) : closedEdges.start(writingMode);
>+    float leftEdgeMove = leftEdgeOnFragment ? visualLeftInset : 0.f;
>+    float rightEdgeMove = rightEdgeOnFragment ? -visualRightInset : 0.f;
>+
>+    // When the whole decoration lives on this fragment, the part of the inset that moves both visual
>+    // edges the same way is an inline-axis shift of the decoration as a whole. Applying that shift to
>+    // every painted piece keeps a symmetric inset a rigid shift of the decoration - including the seam
>+    // between bidi runs - instead of pinning that interior seam. The remaining per-edge movement is the
>+    // extend/trim overhang, applied only at the piece that actually reaches that visual edge; interior
>+    // pieces (e.g. superscripts/subscripts at other baselines) get only the whole-decoration shift, so
>+    // they stay put for a pure extend/trim. (skip-ink needs no adjustment: its gaps are measured relative
>+    // to the underline's bounding box, which already tracks boxOrigin.)
>+    float decorationInlineShift = (leftEdgeOnFragment && rightEdgeOnFragment) ? (leftEdgeMove + rightEdgeMove) / 2.f : 0.f;
>+    bool reachesVisualLeft = leftEdgeOnFragment && ownsLineLeftEdge && (isLTR ? ownsLogicalStart : ownsLogicalEnd);
>+    bool reachesVisualRight = rightEdgeOnFragment && ownsLineRightEdge && (isLTR ? ownsLogicalEnd : ownsLogicalStart);
>+    float leftOverhang = reachesVisualLeft ? leftEdgeMove - decorationInlineShift : 0.f;
>+    float rightOverhang = reachesVisualRight ? rightEdgeMove - decorationInlineShift : 0.f;
>+
>+    float adjustedLeft = boxOrigin.x() + decorationInlineShift + leftOverhang;
>+    float adjustedRight = boxOrigin.x() + width + decorationInlineShift + rightOverhang;
>+    boxOrigin.setX(adjustedLeft);
>+    width = std::max(0.f, adjustedRight - adjustedLeft);
>+    return { boxOrigin, width };
>+}
>+
> void TextBoxPainter::paintBackgroundDecorations(TextDecorationPainter& decorationPainter, const StyledMarkedText& markedText, const FloatRect& textBoxPaintRect)
> {
>     if (m_isCombinedText)
>@@ -934,10 +1020,11 @@ void TextBoxPainter::paintBackgroundDecorations(TextDecorationPainter& decoratio
>                 return baseOffset - wavyOffset;
>             };
> 
>+            auto [insetBoxOrigin, insetWidth] = insetAdjustedDecorationLocationAndWidth(decoratingBox, markedText);
>             return TextDecorationPainter::BackgroundDecorationGeometry {
>                 textOriginFromPaintRect(textBoxPaintRect),
>-                decoratingBox.location,
>-                decoratingBox.contentWidth,
>+                insetBoxOrigin,
>+                insetWidth,
>                 textDecorationThickness,
>                 underlineOffset(),
>                 overlineOffset(),
>@@ -1019,8 +1106,9 @@ void TextBoxPainter::paintForegroundDecorations(TextDecorationPainter& decoratio
> 
>         auto textDecorationThickness = resolveTextDecorationThicknessForPaintingBox(decoratingBox.textDecorationStyles.linethrough.thickness, decoratingBox.style.get(), deviceScaleFactor);
>         auto linethroughCenter = computedLinethroughCenter(decoratingBox.style.get(), textDecorationThickness, computedAutoTextDecorationThickness(decoratingBox.style.get(), deviceScaleFactor));
>-        decorationPainter.paintForegroundDecorations({ decoratingBox.location
>-            , decoratingBox.contentWidth
>+        auto [insetBoxOrigin, insetWidth] = insetAdjustedDecorationLocationAndWidth(decoratingBox, markedText);
>+        decorationPainter.paintForegroundDecorations({ insetBoxOrigin
>+            , insetWidth
>             , textDecorationThickness
>             , linethroughCenter
>             , wavyStrokeParameters(decoratingBox.style->computedFontSize()) }, decoratingBox.textDecorationStyles);
>diff --git a/Source/WebCore/rendering/TextBoxPainter.h b/Source/WebCore/rendering/TextBoxPainter.h
>index 97b2d2b37a8d..023c7ff8a9d2 100644
>--- a/Source/WebCore/rendering/TextBoxPainter.h
>+++ b/Source/WebCore/rendering/TextBoxPainter.h
>@@ -103,6 +103,13 @@ protected:
>     void collectDecoratingBoxesForBackgroundPainting(DecoratingBoxList&, const InlineIterator::TextBoxIterator&, const FloatRect& textBoxRect, const TextDecorationPainter::Styles&);
>     void collectDecoratingBoxesForForegroundPainting(DecoratingBoxList&, const InlineIterator::TextBoxIterator&, const FloatRect& textBoxRect, const TextDecorationPainter::Styles&);
> 
>+    // Applies 'text-decoration-inset' to a decorating box, returning the decoration's adjusted
>+    // logical origin and inline length. Honors box-decoration-break (via the inline box's closed
>+    // edges) so the start inset only affects the first fragment and the end inset the last, and shares
>+    // a symmetric inset's translation across bidi runs / marked-text pieces while applying the
>+    // extend/trim overhang only at the piece that reaches the decoration's visual edge.
>+    std::pair<FloatPoint, float> insetAdjustedDecorationLocationAndWidth(const DecoratingBox&, const StyledMarkedText&) const;
>+
>     // FIXME: We could just talk to the display box directly.
>     const InlineIterator::BoxModernPath m_textBox;
>     const CheckedRef<const RenderText> m_renderer;
>diff --git a/Source/WebCore/rendering/TextDecorationPainter.cpp b/Source/WebCore/rendering/TextDecorationPainter.cpp
>index f47d6fb8fb36..352f4e240f48 100644
>--- a/Source/WebCore/rendering/TextDecorationPainter.cpp
>+++ b/Source/WebCore/rendering/TextDecorationPainter.cpp
>@@ -34,6 +34,7 @@
> #include "RenderText.h"
> #include "StyleAppleColorFilter.h"
> #include "StyleComputedStyle+GettersInlines.h"
>+#include "StyleTextDecorationInset.h"
> #include "StyleTextDecorationLine.h"
> #include "TextBoxPainter.h"
> #include "TextRun.h"
>@@ -178,7 +179,8 @@ bool TextDecorationPainter::Styles::operator==(const Styles& other) const
> {
>     return underline.color == other.underline.color && overline.color == other.overline.color && linethrough.color == other.linethrough.color
>         && underline.decorationStyle == other.underline.decorationStyle && overline.decorationStyle == other.overline.decorationStyle && linethrough.decorationStyle == other.linethrough.decorationStyle
>-        && underline.thickness == other.underline.thickness && overline.thickness == other.overline.thickness && linethrough.thickness == other.linethrough.thickness;
>+        && underline.thickness == other.underline.thickness && overline.thickness == other.overline.thickness && linethrough.thickness == other.linethrough.thickness
>+        && inset == other.inset && boxDecorationBreak == other.boxDecorationBreak;
> }
> 
> TextDecorationPainter::TextDecorationPainter(GraphicsContext& context, const FontCascade& font, const Style::TextShadows& shadow, const Style::AppleColorFilter& colorFilter, bool isPrinting, WritingMode writingMode)
>@@ -326,6 +328,11 @@ static void collectStylesForRenderer(TextDecorationPainter::Styles& result, cons
>         if (!decorations.containsAny({ Style::TextDecorationLine::Flag::Underline, Style::TextDecorationLine::Flag::Overline, Style::TextDecorationLine::Flag::LineThrough }))
>             return;
> 
>+        if (!result.inset) {
>+            result.inset = style.textDecorationInset();
>+            result.boxDecorationBreak = style.boxDecorationBreak();
>+        }
>+
>         auto color = TextDecorationPainter::decorationColor(style, paintBehavior);
>         auto decorationStyle = style.textDecorationStyle();
>         auto thickness = style.textDecorationThickness();
>diff --git a/Source/WebCore/rendering/TextDecorationPainter.h b/Source/WebCore/rendering/TextDecorationPainter.h
>index b725dc9a5065..c026f1245d72 100644
>--- a/Source/WebCore/rendering/TextDecorationPainter.h
>+++ b/Source/WebCore/rendering/TextDecorationPainter.h
>@@ -27,6 +27,7 @@
> #include "GraphicsContext.h"
> #include "InlineTextBoxStyle.h"
> #include "RenderStyleConstants.h"
>+#include "StyleTextDecorationInset.h"
> #include "StyleTextDecorationThickness.h"
> #include <wtf/OptionSet.h>
> 
>@@ -61,6 +62,9 @@ public:
>         DecorationStyleAndColor underline;
>         DecorationStyleAndColor overline;
>         DecorationStyleAndColor linethrough;
>+
>+        std::optional<Style::TextDecorationInset> inset;
>+        BoxDecorationBreak boxDecorationBreak { BoxDecorationBreak::Slice };
>     };
>     struct BackgroundDecorationGeometry {
>         FloatPoint textOrigin;
>diff --git a/Source/WebCore/style/InlineTextBoxStyle.cpp b/Source/WebCore/style/InlineTextBoxStyle.cpp
>index c1b0291740e2..9229c856b98a 100644
>--- a/Source/WebCore/style/InlineTextBoxStyle.cpp
>+++ b/Source/WebCore/style/InlineTextBoxStyle.cpp
>@@ -36,6 +36,7 @@
> #include "RenderElementInlines.h"
> #include "RenderInline.h"
> #include "RenderObjectInlines.h"
>+#include "StyleTextDecorationInset.h"
> 
> namespace WebCore {
> 
>@@ -222,6 +223,18 @@ static InkOverflowForDecorations computedInkOverflowForDecorations(const Style::
>         overflowResult.extendTop(-rect.y());
>         overflowResult.extendBottom(rect.maxY() - height);
>     }
>+
>+    // text-decoration-inset moves the decoration's endpoints along the inline axis. A negative inset
>+    // extends the line outward past the text box, so that overhang must be part of the ink overflow
>+    // or it gets clipped / left unrepainted. A positive inset (and 'auto', which only trims inward)
>+    // needs no expansion. We expand both inline edges by the largest outward amount, which is a safe
>+    // superset regardless of writing mode / direction.
>+    auto outwardInset = std::max<float>({ 0.f, -lineStyle.textDecorationInset().resolvedStart(lineStyle, 0.f), -lineStyle.textDecorationInset().resolvedEnd(lineStyle, 0.f) });
>+    if (outwardInset) {
>+        overflowResult.left() = std::max(overflowResult.left(), LayoutUnit(ceilf(outwardInset)));
>+        overflowResult.right() = std::max(overflowResult.right(), LayoutUnit(ceilf(outwardInset)));
>+    }
>+
>     return overflowResult;
> }
> 
>diff --git a/Source/WebCore/style/PropertyAllowlist.cpp b/Source/WebCore/style/PropertyAllowlist.cpp
>index 77e95a3fc266..e58cb2b4a5fa 100644
>--- a/Source/WebCore/style/PropertyAllowlist.cpp
>+++ b/Source/WebCore/style/PropertyAllowlist.cpp
>@@ -58,6 +58,7 @@ bool isValidHighlightStyleProperty(CSSPropertyID id)
>     case CSSPropertyStrokeWidth:
>     case CSSPropertyTextDecoration:
>     case CSSPropertyTextDecorationColor:
>+    case CSSPropertyTextDecorationInset:
>     case CSSPropertyTextDecorationLine:
>     case CSSPropertyTextDecorationSkip:
>     case CSSPropertyTextDecorationSkipInk:
>@@ -180,6 +181,7 @@ bool isValidCueStyleProperty(CSSPropertyID id)
>     case CSSPropertyWhiteSpaceCollapse:
>     case CSSPropertyTextCombineUpright:
>     case CSSPropertyTextDecorationColor:
>+    case CSSPropertyTextDecorationInset:
>     case CSSPropertyTextDecorationLine:
>     case CSSPropertyTextDecorationStyle:
>     case CSSPropertyTextDecorationThickness:
>@@ -235,6 +237,7 @@ bool isValidCueSelectorStyleProperty(CSSPropertyID id)
>     case CSSPropertyWhiteSpaceCollapse:
>     case CSSPropertyTextCombineUpright:
>     case CSSPropertyTextDecorationColor:
>+    case CSSPropertyTextDecorationInset:
>     case CSSPropertyTextDecorationLine:
>     case CSSPropertyTextDecorationStyle:
>     case CSSPropertyTextDecorationThickness:
>diff --git a/Source/WebCore/style/StyleBuilderCustom.h b/Source/WebCore/style/StyleBuilderCustom.h
>index 7d9940d4cc7d..53ea036fdabc 100644
>--- a/Source/WebCore/style/StyleBuilderCustom.h
>+++ b/Source/WebCore/style/StyleBuilderCustom.h
>@@ -176,6 +176,7 @@ inline SingleAnimationTimeline forwardInheritedValue(const SingleAnimationTimeli
> inline SingleTransitionProperty forwardInheritedValue(const SingleTransitionProperty& value) { auto copy = value; return copy; }
> inline StrokeWidth forwardInheritedValue(const StrokeWidth& value) { auto copy = value; return copy; }
> inline TabSize forwardInheritedValue(const TabSize& value) { auto copy = value; return copy; }
>+inline TextDecorationInset forwardInheritedValue(const TextDecorationInset& value) { auto copy = value; return copy; }
> inline TextDecorationLine forwardInheritedValue(const TextDecorationLine& value) { auto copy = value; return copy; }
> inline TextDecorationThickness forwardInheritedValue(const TextDecorationThickness& value) { auto copy = value; return copy; }
> inline TextEmphasisStyle forwardInheritedValue(const TextEmphasisStyle& value) { auto copy = value; return copy; }
>diff --git a/Source/WebCore/style/StyleDifference.cpp b/Source/WebCore/style/StyleDifference.cpp
>index fc7d4fcd1864..87e676b47769 100644
>--- a/Source/WebCore/style/StyleDifference.cpp
>+++ b/Source/WebCore/style/StyleDifference.cpp
>@@ -100,7 +100,8 @@ public:
> 
>             if (&a.nonInheritedData() != &b.nonInheritedData() && a.nonInheritedData().rareData.ptr() != b.nonInheritedData().rareData.ptr()) {
>                 if (a.nonInheritedData().rareData->textDecorationStyle != b.nonInheritedData().rareData->textDecorationStyle
>-                    || a.nonInheritedData().rareData->textDecorationThickness != b.nonInheritedData().rareData->textDecorationThickness)
>+                    || a.nonInheritedData().rareData->textDecorationThickness != b.nonInheritedData().rareData->textDecorationThickness
>+                    || a.nonInheritedData().rareData->textDecorationInset != b.nonInheritedData().rareData->textDecorationInset)
>                     return true;
>             }
> 
>@@ -781,7 +782,7 @@ public:
>             // Don't return true; keep looking for another change.
>         }
> 
>-        if (a.textDecorationStyle != b.textDecorationStyle || a.textDecorationColor != b.textDecorationColor || a.textDecorationThickness != b.textDecorationThickness)
>+        if (a.textDecorationStyle != b.textDecorationStyle || a.textDecorationColor != b.textDecorationColor || a.textDecorationThickness != b.textDecorationThickness || a.textDecorationInset != b.textDecorationInset)
>             return true;
> 
>         return false;
>diff --git a/Source/WebCore/style/computed/StyleComputedStyleBase.h b/Source/WebCore/style/computed/StyleComputedStyleBase.h
>index 99f205cc0eef..f340a3150be0 100644
>--- a/Source/WebCore/style/computed/StyleComputedStyleBase.h
>+++ b/Source/WebCore/style/computed/StyleComputedStyleBase.h
>@@ -353,6 +353,7 @@ struct StrokeWidth;
> struct TabSize;
> struct TextAutospace;
> struct TextBoxEdge;
>+struct TextDecorationInset;
> struct TextDecorationLine;
> struct TextDecorationThickness;
> struct TextEmphasisPosition;
>diff --git a/Source/WebCore/style/computed/data/StyleNonInheritedRareData.cpp b/Source/WebCore/style/computed/data/StyleNonInheritedRareData.cpp
>index d96037905a9d..6016bbe63072 100644
>--- a/Source/WebCore/style/computed/data/StyleNonInheritedRareData.cpp
>+++ b/Source/WebCore/style/computed/data/StyleNonInheritedRareData.cpp
>@@ -79,6 +79,7 @@ NonInheritedRareData::NonInheritedRareData()
>     , offsetAnchor(ComputedStyle::initialOffsetAnchor())
>     , offsetRotate(ComputedStyle::initialOffsetRotate())
>     , textDecorationColor(ComputedStyle::initialTextDecorationColor())
>+    , textDecorationInset(ComputedStyle::initialTextDecorationInset())
>     , textDecorationThickness(ComputedStyle::initialTextDecorationThickness())
>     , scrollTimelines { CSS::Keyword::None { } }
>     , viewTimelines { CSS::Keyword::None { } }
>@@ -187,6 +188,7 @@ inline NonInheritedRareData::NonInheritedRareData(const NonInheritedRareData& o)
>     , offsetAnchor(o.offsetAnchor)
>     , offsetRotate(o.offsetRotate)
>     , textDecorationColor(o.textDecorationColor)
>+    , textDecorationInset(o.textDecorationInset)
>     , textDecorationThickness(o.textDecorationThickness)
>     , scrollTimelines(o.scrollTimelines)
>     , viewTimelines(o.viewTimelines)
>@@ -301,6 +303,7 @@ bool NonInheritedRareData::operator==(const NonInheritedRareData& o) const
>         && offsetAnchor == o.offsetAnchor
>         && offsetRotate == o.offsetRotate
>         && textDecorationThickness == o.textDecorationThickness
>+        && textDecorationInset == o.textDecorationInset
>         && scrollTimelines == o.scrollTimelines
>         && viewTimelines == o.viewTimelines
>         && timelineScope == o.timelineScope
>@@ -444,6 +447,7 @@ void NonInheritedRareData::dumpDifferences(TextStream& ts, const NonInheritedRar
>     LOG_IF_DIFFERENT(offsetRotate);
> 
>     LOG_IF_DIFFERENT(textDecorationThickness);
>+    LOG_IF_DIFFERENT(textDecorationInset);
> 
>     LOG_IF_DIFFERENT(scrollTimelines);
>     LOG_IF_DIFFERENT(viewTimelines);
>diff --git a/Source/WebCore/style/computed/data/StyleNonInheritedRareData.h b/Source/WebCore/style/computed/data/StyleNonInheritedRareData.h
>index 47ec3e37fae9..d54923c86b70 100644
>--- a/Source/WebCore/style/computed/data/StyleNonInheritedRareData.h
>+++ b/Source/WebCore/style/computed/data/StyleNonInheritedRareData.h
>@@ -71,6 +71,7 @@
> #include <WebCore/StyleShapeImageThreshold.h>
> #include <WebCore/StyleShapeMargin.h>
> #include <WebCore/StyleShapeOutside.h>
>+#include <WebCore/StyleTextDecorationInset.h>
> #include <WebCore/StyleTextDecorationThickness.h>
> #include <WebCore/StyleTimelineTriggers.h>
> #include <WebCore/StyleTouchAction.h>
>@@ -182,6 +183,7 @@ public:
>     OffsetRotate offsetRotate;
> 
>     Color textDecorationColor;
>+    TextDecorationInset textDecorationInset;
>     TextDecorationThickness textDecorationThickness;
> 
>     ScrollTimelines scrollTimelines;
>diff --git a/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.cpp b/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.cpp
>new file mode 100644
>index 000000000000..82475a879b92
>--- /dev/null
>+++ b/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.cpp
>@@ -0,0 +1,75 @@
>+/*
>+ * Copyright (C) 2026 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "StyleTextDecorationInset.h"
>+
>+#include "StyleBuilderChecking.h"
>+#include "StyleComputedStyle+GettersInlines.h"
>+#include "StylePrimitiveNumericTypes+CSSValueConversion.h"
>+#include "StylePrimitiveNumericTypes+Evaluation.h"
>+
>+namespace WebCore {
>+namespace Style {
>+
>+using namespace CSS::Literals;
>+
>+float TextDecorationInset::resolvedStart(const Style::ComputedStyle& style, float autoValue) const
>+{
>+    if (auto pair = tryValue())
>+        return Style::evaluate<float>(pair->first(), style.usedZoomForLength());
>+    return autoValue;
>+}
>+
>+float TextDecorationInset::resolvedEnd(const Style::ComputedStyle& style, float autoValue) const
>+{
>+    if (auto pair = tryValue())
>+        return Style::evaluate<float>(pair->second(), style.usedZoomForLength());
>+    return autoValue;
>+}
>+
>+// MARK: - Conversion
>+
>+auto CSSValueConversion<TextDecorationInsetPair>::operator()(BuilderState& state, const CSSValue& value) -> TextDecorationInsetPair
>+{
>+    using Length = Style::Length<CSS::AllUnzoomed>;
>+
>+    if (RefPtr primitiveValue = dynamicDowncast<CSSPrimitiveValue>(value)) {
>+        auto length = toStyleFromCSSValue<Length>(state, *primitiveValue);
>+        return { length, length };
>+    }
>+
>+    auto pair = requiredPairDowncast<CSSPrimitiveValue>(state, value);
>+    if (!pair)
>+        return { 0_css_px, 0_css_px };
>+
>+    return {
>+        toStyleFromCSSValue<Length>(state, pair->first),
>+        toStyleFromCSSValue<Length>(state, pair->second),
>+    };
>+}
>+
>+} // namespace Style
>+} // namespace WebCore
>diff --git a/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.h b/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.h
>new file mode 100644
>index 000000000000..2170865a4df2
>--- /dev/null
>+++ b/Source/WebCore/style/values/text-decoration/StyleTextDecorationInset.h
>@@ -0,0 +1,84 @@
>+/*
>+ * Copyright (C) 2026 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
>+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
>+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
>+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
>+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
>+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#pragma once
>+
>+#include <WebCore/StylePrimitiveNumericTypes.h>
>+#include <WebCore/StyleValueTypes.h>
>+
>+namespace WebCore {
>+namespace Style {
>+using TextDecorationInsetPair = MinimallySerializingSpaceSeparatedPair<Length<CSS::AllUnzoomed>>;
>+}
>+}
>+
>+// text-decoration-inset stores 'auto' or a length pair, so ValueOrKeyword needs a Markable
>+// representation of the pair; the pair is empty exactly when its first length is empty.
>+namespace WTF {
>+template<> struct MarkableTraits<WebCore::Style::TextDecorationInsetPair> {
>+    using Pair = WebCore::Style::TextDecorationInsetPair;
>+    using Length = WebCore::Style::Length<WebCore::CSS::AllUnzoomed>;
>+    static bool isEmptyValue(const Pair& value) { return MarkableTraits<Length>::isEmptyValue(value.first()); }
>+    static Pair emptyValue() { return { MarkableTraits<Length>::emptyValue(), MarkableTraits<Length>::emptyValue() }; }
>+};
>+}
>+
>+namespace WebCore {
>+namespace Style {
>+
>+// <'text-decoration-inset'> = auto | <length>{1,2}
>+// The first value applies to the start endpoint, the second to the end endpoint of the line
>+// decorations; a single value applies to both. Positive values move an endpoint inward (trimming
>+// the decoration), negative values move it outward (extending it). 'auto' lets the UA choose an
>+// inset so that adjacent identical underlined elements do not appear to share a single continuous
>+// underline. Note that 'auto' is distinct from '0'.
>+// https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property
>+struct TextDecorationInset : ValueOrKeyword<TextDecorationInsetPair, CSS::Keyword::Auto> {
>+    using Base::Base;
>+
>+    TextDecorationInset(CSS::ValueLiteral<CSS::LengthUnit::Px> literal)
>+        : Base(Value { Length<CSS::AllUnzoomed> { literal }, Length<CSS::AllUnzoomed> { literal } })
>+    {
>+    }
>+
>+    bool isAuto() const { return isKeyword(); }
>+
>+    // Resolves the start/end inset to used CSS pixels. For 'auto', returns the UA-chosen autoValue
>+    // supplied by the caller (which depends on the decorating box's font).
>+    float resolvedStart(const Style::ComputedStyle&, float autoValue) const;
>+    float resolvedEnd(const Style::ComputedStyle&, float autoValue) const;
>+};
>+
>+// MARK: - Conversion
>+
>+// Conversion of the 'auto' keyword is handled generically (CSSValueConversion<ValueOrKeywordDerived>);
>+// only the length-pair value needs the usual pair unpacking.
>+template<> struct CSSValueConversion<TextDecorationInsetPair> {
>+    auto operator()(BuilderState&, const CSSValue&) -> TextDecorationInsetPair;
>+};
>+
>+} // namespace Style
>+} // namespace WebCore
>+
>+DEFINE_VARIANT_LIKE_CONFORMANCE(WebCore::Style::TextDecorationInset)
>diff --git a/LayoutTests/TestExpectations b/LayoutTests/TestExpectations
>index 124e7b0cfd34..9dfb7d9e8c5e 100644
>--- a/LayoutTests/TestExpectations
>+++ b/LayoutTests/TestExpectations
>@@ -4683,31 +4683,14 @@ webkit.org/b/244813 imported/w3c/web-platform-tests/css/css-text-decor/text-deco
> webkit.org/b/244813 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-skip-spaces-009.html [ ImageOnlyFailure ]
> imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-thickness-length-rounding-001.html [ ImageOnlyFailure ]
> imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-thickness-length-rounding-002.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-001.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-002.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-003.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-004.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-005.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-006.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-007.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-008.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-009.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-010.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-011.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-012.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-013.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-014.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-015.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-016.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-017.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-018.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-019.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-020.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-021.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-022.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-023.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-024.html [ ImageOnlyFailure ]
>-webkit.org/b/304166 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-025.html [ ImageOnlyFailure ]
>+
>+# fractional-position endpoint rounds up to a device pixel
>+webkit.org/b/244813 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-009.html [ ImageOnlyFailure ]
>+webkit.org/b/244813 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-014.html [ ImageOnlyFailure ]
>+
>+# Not a text-decoration-inset bug: a pre-existing ~1px vertical decoration-position difference in a
>+# columns:2 multicol context with inline vertical borders. Reproduces with the feature disabled.
>+webkit.org/b/304168 imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-025.html [ ImageOnlyFailure ]
> imported/w3c/web-platform-tests/css/css-text-decor/text-emphasis-color-property-001.html [ ImageOnlyFailure ]
> imported/w3c/web-platform-tests/css/css-text-decor/text-emphasis-color-property-001a.html [ ImageOnlyFailure ]
> imported/w3c/web-platform-tests/css/css-text-decor/text-emphasis-color-property-001b.html [ ImageOnlyFailure ]
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-cascade/all-prop-initial-xml-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-cascade/all-prop-initial-xml-expected.txt
>index 1ba82c0506ca..4d78b0c97916 100644
>--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-cascade/all-prop-initial-xml-expected.txt
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-cascade/all-prop-initial-xml-expected.txt
>@@ -351,6 +351,7 @@ PASS text-box-edge
> PASS text-box-trim
> PASS text-combine-upright
> PASS text-decoration-color
>+PASS text-decoration-inset
> PASS text-decoration-line
> PASS text-decoration-skip-ink
> PASS text-decoration-style
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-computed-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-computed-expected.txt
>index 007652014e8b..49ace8ee9180 100644
>--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-computed-expected.txt
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-computed-expected.txt
>@@ -1,12 +1,12 @@
> 
>-FAIL Property text-decoration-inset value '0px' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '0' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '0px 0px' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '0.5em' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '-1em' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '-1ch -1ch' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '1px 2px' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value '1ch -1ch' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value 'calc(1em / 4) calc(-1ch)' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>-FAIL Property text-decoration-inset value 'auto' assert_true: text-decoration-inset doesn't seem to be supported in the computed style expected true got false
>+PASS Property text-decoration-inset value '0px'
>+PASS Property text-decoration-inset value '0'
>+PASS Property text-decoration-inset value '0px 0px'
>+PASS Property text-decoration-inset value '0.5em'
>+PASS Property text-decoration-inset value '-1em'
>+PASS Property text-decoration-inset value '-1ch -1ch'
>+PASS Property text-decoration-inset value '1px 2px'
>+PASS Property text-decoration-inset value '1ch -1ch'
>+PASS Property text-decoration-inset value 'calc(1em / 4) calc(-1ch)'
>+PASS Property text-decoration-inset value 'auto'
> 
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-valid-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-valid-expected.txt
>index e392322573bf..115049c2bf6a 100644
>--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-valid-expected.txt
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/parsing/text-decoration-inset-valid-expected.txt
>@@ -1,12 +1,12 @@
> 
>-FAIL e.style['text-decoration-inset'] = "0px" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "0" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "0px 0px" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "0.5em" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "-1em" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "-1ch -1ch" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "1px 2px" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "1ch -1ch" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "calc(1em / 4) calc(-1ch)" should set the property value assert_not_equals: property should be set got disallowed value ""
>-FAIL e.style['text-decoration-inset'] = "auto" should set the property value assert_not_equals: property should be set got disallowed value ""
>+PASS e.style['text-decoration-inset'] = "0px" should set the property value
>+PASS e.style['text-decoration-inset'] = "0" should set the property value
>+PASS e.style['text-decoration-inset'] = "0px 0px" should set the property value
>+PASS e.style['text-decoration-inset'] = "0.5em" should set the property value
>+PASS e.style['text-decoration-inset'] = "-1em" should set the property value
>+PASS e.style['text-decoration-inset'] = "-1ch -1ch" should set the property value
>+PASS e.style['text-decoration-inset'] = "1px 2px" should set the property value
>+PASS e.style['text-decoration-inset'] = "1ch -1ch" should set the property value
>+PASS e.style['text-decoration-inset'] = "calc(1em / 4) calc(-1ch)" should set the property value
>+PASS e.style['text-decoration-inset'] = "auto" should set the property value
> 
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk-expected.html
>new file mode 100644
>index 000000000000..b15cfb16b631
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk-expected.html
>@@ -0,0 +1,11 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: auto separates adjacent underlined CJK runs (reference)</title>
>+<style>
>+    body { margin: 20px; background: white; }
>+    div { font: 60px/1.5 sans-serif; color: black; }
>+    /* WebKit's 'auto' amount is font-size/8 = 0.125em, applied to both endpoints. */
>+    u { text-decoration-line: underline; text-decoration-color: blue; text-underline-position: under; text-decoration-inset: 0.125em; }
>+</style>
>+<p>The underlines for the two elements should be visibly separated by a gap:</p>
>+<div lang="zh"><u>ç³äº</u><u>è¾ä¿ä¿</u></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk.html
>new file mode 100644
>index 000000000000..b063e0dbdf52
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-cjk.html
>@@ -0,0 +1,12 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: auto separates adjacent underlined CJK runs</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="'text-decoration-inset: auto' insets each decorating box's endpoints by a UA-chosen amount so two adjacent underlined elements do not appear to share a single underline (the spec's CJK example, &lt;u&gt;ç³äº&lt;/u&gt;&lt;u&gt;è¾ä¿ä¿&lt;/u&gt;). WebKit's auto amount is font-size/8, so 'auto' must render identically to '0.125em'.">
>+<style>
>+    body { margin: 20px; background: white; }
>+    div { font: 60px/1.5 sans-serif; color: black; }
>+    u { text-decoration-line: underline; text-decoration-color: blue; text-underline-position: under; text-decoration-inset: auto; }
>+</style>
>+<p>The underlines for the two elements should be visibly separated by a gap:</p>
>+<div lang="zh"><u>ç³äº</u><u>è¾ä¿ä¿</u></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-expected-mismatch.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-expected-mismatch.html
>new file mode 100644
>index 000000000000..6f84e07b55a3
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto-expected-mismatch.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: auto trims the underline (mismatch reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u>abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto.html
>new file mode 100644
>index 000000000000..bfd95aec5e59
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-auto.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: auto trims the underline</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset: auto insets the endpoints by a UA-chosen amount, so the underline differs from an un-inset one.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u style="text-decoration-inset: auto">abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break-expected-mismatch.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break-expected-mismatch.html
>new file mode 100644
>index 000000000000..2579e1960011
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break-expected-mismatch.html
>@@ -0,0 +1,9 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset honors box-decoration-break: slice (mismatch reference uses clone)</title>
>+<style>
>+    body { margin: 20px; font: 40px/1.5 monospace; }
>+    div { width: 200px; }
>+    span { text-decoration-line: underline; text-decoration-inset: 8px; -webkit-box-decoration-break: clone; }
>+</style>
>+<div><span>aaaaa bbbbb</span></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break.html
>new file mode 100644
>index 000000000000..7ff93227f454
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-box-decoration-break.html
>@@ -0,0 +1,11 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset honors box-decoration-break: slice</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="With box-decoration-break: slice, the start inset applies only to the first line fragment's start and the end inset only to the last fragment's end; this differs from box-decoration-break: clone, which insets every fragment on both sides.">
>+<style>
>+    body { margin: 20px; font: 40px/1.5 monospace; }
>+    div { width: 200px; }
>+    span { text-decoration-line: underline; text-decoration-inset: 8px; -webkit-box-decoration-break: slice; }
>+</style>
>+<div><span>aaaaa bbbbb</span></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed-expected.txt
>new file mode 100644
>index 000000000000..4c3f41c99682
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed-expected.txt
>@@ -0,0 +1,20 @@
>+
>+PASS text-decoration-inset initial computed value is '0px'
>+PASS text-decoration-inset: auto
>+PASS text-decoration-inset: 0 computes to '0px'
>+PASS text-decoration-inset: 5px
>+PASS text-decoration-inset: two equal values serialize as one
>+PASS text-decoration-inset: 1px 2px
>+PASS text-decoration-inset: negative value (extends the decoration)
>+PASS text-decoration-inset: mixed sign start/end
>+PASS text-decoration-inset: em resolves against font-size
>+PASS text-decoration-inset: calc resolves to an absolute length
>+PASS text-decoration-inset: calc with em resolves against font-size
>+PASS text-decoration-inset: absolute units resolve to px
>+PASS text-decoration-inset: negative em resolves to px
>+PASS text-decoration-inset: two values, one a calc
>+PASS text-decoration-inset: two equal computed lengths serialize as one
>+PASS text-decoration-inset ignores invalid values (auto cannot combine with a length)
>+PASS text-decoration-inset is not inherited
>+PASS text-decoration-inset: inherit resolves to the parent value
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed.html
>new file mode 100644
>index 000000000000..17b0a8df5ca2
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-computed.html
>@@ -0,0 +1,96 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: parsing and computed value of text-decoration-inset</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset accepts auto or one-or-two <length> values, is not inherited, and computes lengths to absolute values.">
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<div id="target" style="font-size: 16px"></div>
>+<div id="parent" style="text-decoration-inset: 4px"><div id="child"></div></div>
>+<script>
>+function computedValueFor(value) {
>+    var target = document.getElementById("target");
>+    target.style.textDecorationInset = "";
>+    target.style.textDecorationInset = value;
>+    return getComputedStyle(target).textDecorationInset;
>+}
>+
>+test(function() {
>+    assert_equals(computedValueFor(""), "0px");
>+}, "text-decoration-inset initial computed value is '0px'");
>+
>+test(function() {
>+    assert_equals(computedValueFor("auto"), "auto");
>+}, "text-decoration-inset: auto");
>+
>+test(function() {
>+    assert_equals(computedValueFor("0"), "0px");
>+}, "text-decoration-inset: 0 computes to '0px'");
>+
>+test(function() {
>+    assert_equals(computedValueFor("5px"), "5px");
>+}, "text-decoration-inset: 5px");
>+
>+test(function() {
>+    assert_equals(computedValueFor("5px 5px"), "5px");
>+}, "text-decoration-inset: two equal values serialize as one");
>+
>+test(function() {
>+    assert_equals(computedValueFor("1px 2px"), "1px 2px");
>+}, "text-decoration-inset: 1px 2px");
>+
>+test(function() {
>+    assert_equals(computedValueFor("-3px"), "-3px");
>+}, "text-decoration-inset: negative value (extends the decoration)");
>+
>+test(function() {
>+    assert_equals(computedValueFor("1px -2px"), "1px -2px");
>+}, "text-decoration-inset: mixed sign start/end");
>+
>+test(function() {
>+    assert_equals(computedValueFor("2em"), "32px");
>+}, "text-decoration-inset: em resolves against font-size");
>+
>+test(function() {
>+    assert_equals(computedValueFor("calc(10px - 8px)"), "2px");
>+}, "text-decoration-inset: calc resolves to an absolute length");
>+
>+test(function() {
>+    assert_equals(computedValueFor("calc(2em - 8px)"), "24px");
>+}, "text-decoration-inset: calc with em resolves against font-size");
>+
>+test(function() {
>+    assert_equals(computedValueFor("1in"), "96px");
>+}, "text-decoration-inset: absolute units resolve to px");
>+
>+test(function() {
>+    assert_equals(computedValueFor("-1em"), "-16px");
>+}, "text-decoration-inset: negative em resolves to px");
>+
>+test(function() {
>+    assert_equals(computedValueFor("10px calc(1em + 4px)"), "10px 20px");
>+}, "text-decoration-inset: two values, one a calc");
>+
>+test(function() {
>+    assert_equals(computedValueFor("2em 2em"), "32px");
>+}, "text-decoration-inset: two equal computed lengths serialize as one");
>+
>+test(function() {
>+    var target = document.getElementById("target");
>+    target.style.textDecorationInset = "3px";
>+    target.style.textDecorationInset = "auto 5px";
>+    assert_equals(target.style.textDecorationInset, "3px");
>+}, "text-decoration-inset ignores invalid values (auto cannot combine with a length)");
>+
>+test(function() {
>+    // text-decoration-inset is not inherited: the child computes the initial value even though its parent sets it.
>+    assert_equals(getComputedStyle(document.getElementById("child")).textDecorationInset, "0px");
>+}, "text-decoration-inset is not inherited");
>+
>+test(function() {
>+    // The 'inherit' keyword still explicitly pulls the parent's value.
>+    var child = document.getElementById("child");
>+    child.style.textDecorationInset = "inherit";
>+    assert_equals(getComputedStyle(child).textDecorationInset, "4px");
>+}, "text-decoration-inset: inherit resolves to the parent value");
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid-expected.txt
>new file mode 100644
>index 000000000000..444ef81ced8c
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid-expected.txt
>@@ -0,0 +1,17 @@
>+
>+PASS e.style['text-decoration-inset'] = "otto" should not set the property value
>+PASS e.style['text-decoration-inset'] = "none" should not set the property value
>+PASS e.style['text-decoration-inset'] = "normal" should not set the property value
>+PASS e.style['text-decoration-inset'] = "red" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10deg" should not set the property value
>+PASS e.style['text-decoration-inset'] = "!@#$%" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10 20" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10%" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10px 20%" should not set the property value
>+PASS e.style['text-decoration-inset'] = "calc(10px + 10%)" should not set the property value
>+PASS e.style['text-decoration-inset'] = "auto auto" should not set the property value
>+PASS e.style['text-decoration-inset'] = "auto 10px" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10px auto" should not set the property value
>+PASS e.style['text-decoration-inset'] = "10px 20px 30px" should not set the property value
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid.html
>new file mode 100644
>index 000000000000..79be28b4a364
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-invalid.html
>@@ -0,0 +1,35 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: parsing text-decoration-inset with invalid values</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset supports: auto | <length>{1,2}">
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="/css/support/parsing-testcommon.js"></script>
>+<div id="target"></div>
>+<script>
>+// Nonsense / wrong type.
>+test_invalid_value("text-decoration-inset", "otto");
>+test_invalid_value("text-decoration-inset", "none");
>+test_invalid_value("text-decoration-inset", "normal");
>+test_invalid_value("text-decoration-inset", "red");
>+test_invalid_value("text-decoration-inset", "10deg");
>+test_invalid_value("text-decoration-inset", "!@#$%");
>+
>+// Unitless non-zero number is not a <length>.
>+test_invalid_value("text-decoration-inset", "10");
>+test_invalid_value("text-decoration-inset", "10 20");
>+
>+// Percentages are not accepted (grammar is <length>, not <length-percentage>).
>+test_invalid_value("text-decoration-inset", "10%");
>+test_invalid_value("text-decoration-inset", "10px 20%");
>+test_invalid_value("text-decoration-inset", "calc(10px + 10%)");
>+
>+// 'auto' cannot combine with a length, and only one keyword is allowed.
>+test_invalid_value("text-decoration-inset", "auto auto");
>+test_invalid_value("text-decoration-inset", "auto 10px");
>+test_invalid_value("text-decoration-inset", "10px auto");
>+
>+// At most two <length> values.
>+test_invalid_value("text-decoration-inset", "10px 20px 30px");
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through-expected.html
>new file mode 100644
>index 000000000000..65d2b1d89793
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through-expected.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset applies to line-through (reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><span>abcdef</span></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through.html
>new file mode 100644
>index 000000000000..39ce9b337a04
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-line-through.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset applies to line-through</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset adjusts the line-through endpoints; a large inset trims the line-through away.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; } span { text-decoration-line: line-through; }</style>
>+<p><span style="text-decoration-inset: 1000px">abcdef</span></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap-expected.html
>new file mode 100644
>index 000000000000..a9aa56e4877c
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap-expected.html
>@@ -0,0 +1,12 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset is not re-applied at interior marked-text boundaries (reference)</title>
>+<link rel="stylesheet" href="/fonts/ahem.css">
>+<style>
>+    body { margin: 20px; }
>+    div { font: 40px/1.5 Ahem; color: black; }
>+    /* One continuous underline over the whole element, trimmed 8px only at the outer ends. */
>+    u { text-decoration-line: underline; text-decoration-color: blue; text-underline-position: under; text-decoration-inset: 8px; }
>+    span { color: green; }
>+</style>
>+<div><u>XX<span>XX</span>XX</u></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap.html
>new file mode 100644
>index 000000000000..5941a867ac38
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-marked-text-gap.html
>@@ -0,0 +1,24 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset is not re-applied at interior marked-text boundaries</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="A single underlined element split into several marked-text pieces (here by a selection over the middle) is one continuous decoration: the inset must trim only the element's true start/end endpoints, not the interior boundaries between marked-text pieces.">
>+<link rel="match" href="text-decoration-inset-marked-text-gap-expected.html">
>+<link rel="stylesheet" href="/fonts/ahem.css">
>+<style>
>+    body { margin: 20px; }
>+    div { font: 40px/1.5 Ahem; color: black; }
>+    /* The selection only changes the text color, which keeps the decoration visually continuous
>+       but splits it into separate marked-text pieces during painting. */
>+    #target::selection { color: green; background-color: transparent; }
>+    u { text-decoration-line: underline; text-decoration-color: blue; text-underline-position: under; text-decoration-inset: 8px; }
>+</style>
>+<div><u id="target">XXXXXX</u></div>
>+<script>
>+    const target = document.getElementById("target").firstChild;
>+    const range = new Range();
>+    range.setStart(target, 2);
>+    range.setEnd(target, 4);
>+    getSelection().removeAllRanges();
>+    getSelection().addRange(range);
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative-expected-mismatch.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative-expected-mismatch.html
>new file mode 100644
>index 000000000000..060f1f854dba
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative-expected-mismatch.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: negative text-decoration-inset extends the underline (mismatch reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u>abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative.html
>new file mode 100644
>index 000000000000..d48bce3478a3
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-negative.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: negative text-decoration-inset extends the underline</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="A negative text-decoration-inset moves the endpoints outward, extending the underline beyond the text, so it differs from an un-inset one.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u style="text-decoration-inset: -10px">abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited-expected.html
>new file mode 100644
>index 000000000000..31f7c7b0f41f
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited-expected.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset is not inherited (reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<div><u>abcdef</u></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited.html
>new file mode 100644
>index 000000000000..6e7c99b802da
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-not-inherited.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset is not inherited</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset is not inherited: a large inset on the parent does not affect the child's own underline.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<div style="text-decoration-inset: 1000px"><u>abcdef</u></div>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value-expected.html
>new file mode 100644
>index 000000000000..1121945b90f8
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value-expected.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: a single text-decoration-inset value applies to both endpoints (reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u style="text-decoration-inset: 12px 12px">wwwwwwww</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value.html
>new file mode 100644
>index 000000000000..dad664a35386
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-one-value.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: a single text-decoration-inset value applies to both endpoints</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="A single <length> applies to both the start and end endpoints, i.e. '12px' == '12px 12px'.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u style="text-decoration-inset: 12px">wwwwwwww</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline-expected.html
>new file mode 100644
>index 000000000000..dbd0bb05c56f
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline-expected.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset applies to overline (reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><span>abcdef</span></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline.html
>new file mode 100644
>index 000000000000..7a0291035f60
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-overline.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset applies to overline</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset adjusts the overline endpoints; a large inset trims the overline away.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; } span { text-decoration-line: overline; }</style>
>+<p><span style="text-decoration-inset: 1000px">abcdef</span></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-expected.html
>new file mode 100644
>index 000000000000..36534c8d599d
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-expected.html
>@@ -0,0 +1,8 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset trims the underline inward (reference)</title>
>+<style>
>+    body { margin: 20px; font: 40px/1.5 monospace; }
>+    u { text-decoration-line: none; }
>+</style>
>+<p><u>abc</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-ref.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-ref.html
>new file mode 100644
>index 000000000000..36534c8d599d
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline-ref.html
>@@ -0,0 +1,8 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset trims the underline inward (reference)</title>
>+<style>
>+    body { margin: 20px; font: 40px/1.5 monospace; }
>+    u { text-decoration-line: none; }
>+</style>
>+<p><u>abc</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline.html
>new file mode 100644
>index 000000000000..67969486dc2e
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-trims-underline.html
>@@ -0,0 +1,12 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset trims the underline inward</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<link rel="match" href="text-decoration-inset-trims-underline-ref.html">
>+<meta name="assert" content="A large positive text-decoration-inset trims the underline from both endpoints until nothing is drawn.">
>+<style>
>+    body { margin: 20px; font: 40px/1.5 monospace; }
>+    /* The start and end insets together exceed the underline length, so no underline is drawn. */
>+    u { text-decoration-inset: 1000px; }
>+</style>
>+<p><u>abc</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid-expected.txt
>new file mode 100644
>index 000000000000..9f3f691349dc
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid-expected.txt
>@@ -0,0 +1,24 @@
>+
>+PASS e.style['text-decoration-inset'] = "auto" should set the property value
>+PASS e.style['text-decoration-inset'] = "0px" should set the property value
>+PASS e.style['text-decoration-inset'] = "10px" should set the property value
>+PASS e.style['text-decoration-inset'] = "-10px" should set the property value
>+PASS e.style['text-decoration-inset'] = "0.5em" should set the property value
>+PASS e.style['text-decoration-inset'] = "2em" should set the property value
>+PASS e.style['text-decoration-inset'] = "-3em" should set the property value
>+PASS e.style['text-decoration-inset'] = "100px" should set the property value
>+PASS e.style['text-decoration-inset'] = "1in" should set the property value
>+PASS e.style['text-decoration-inset'] = "2cm" should set the property value
>+PASS e.style['text-decoration-inset'] = "10pt" should set the property value
>+PASS e.style['text-decoration-inset'] = "2rem" should set the property value
>+PASS e.style['text-decoration-inset'] = "calc(10px + 2px)" should set the property value
>+PASS e.style['text-decoration-inset'] = "calc(2em - 5px)" should set the property value
>+PASS e.style['text-decoration-inset'] = "10px 20px" should set the property value
>+PASS e.style['text-decoration-inset'] = "20px 10px" should set the property value
>+PASS e.style['text-decoration-inset'] = "-5px 8px" should set the property value
>+PASS e.style['text-decoration-inset'] = "10px -20px" should set the property value
>+PASS e.style['text-decoration-inset'] = "0px 0px" should set the property value
>+PASS e.style['text-decoration-inset'] = "10px 0px" should set the property value
>+PASS e.style['text-decoration-inset'] = "1em 10px" should set the property value
>+PASS e.style['text-decoration-inset'] = "calc(1px + 1px) 5px" should set the property value
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid.html
>new file mode 100644
>index 000000000000..0224f600ffc8
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-valid.html
>@@ -0,0 +1,40 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: parsing text-decoration-inset with valid values</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset supports: auto | <length>{1,2}">
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="/css/support/parsing-testcommon.js"></script>
>+<div id="target"></div>
>+<script>
>+// Keyword.
>+test_valid_value("text-decoration-inset", "auto");
>+
>+// Single <length>, various units and signs.
>+test_valid_value("text-decoration-inset", "0px");
>+test_valid_value("text-decoration-inset", "10px");
>+test_valid_value("text-decoration-inset", "-10px");
>+test_valid_value("text-decoration-inset", "0.5em");
>+test_valid_value("text-decoration-inset", "2em");
>+test_valid_value("text-decoration-inset", "-3em");
>+test_valid_value("text-decoration-inset", "100px");
>+test_valid_value("text-decoration-inset", "1in");
>+test_valid_value("text-decoration-inset", "2cm");
>+test_valid_value("text-decoration-inset", "10pt");
>+test_valid_value("text-decoration-inset", "2rem");
>+
>+// calc().
>+test_valid_value("text-decoration-inset", "calc(10px + 2px)", "calc(12px)");
>+test_valid_value("text-decoration-inset", "calc(2em - 5px)");
>+
>+// Two <length> values (start end).
>+test_valid_value("text-decoration-inset", "10px 20px");
>+test_valid_value("text-decoration-inset", "20px 10px");
>+test_valid_value("text-decoration-inset", "-5px 8px");
>+test_valid_value("text-decoration-inset", "10px -20px");
>+test_valid_value("text-decoration-inset", "0px 0px", "0px");
>+test_valid_value("text-decoration-inset", "10px 0px");
>+test_valid_value("text-decoration-inset", "1em 10px");
>+test_valid_value("text-decoration-inset", "calc(1px + 1px) 5px", "calc(2px) 5px");
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero-expected.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero-expected.html
>new file mode 100644
>index 000000000000..6995147dde43
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero-expected.html
>@@ -0,0 +1,5 @@
>+<!DOCTYPE html>
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: 0 does not change the decoration (reference)</title>
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u>abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero.html b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero.html
>new file mode 100644
>index 000000000000..3b5e125a0704
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-text-decor/text-decoration-inset-zero.html
>@@ -0,0 +1,7 @@
>+<!DOCTYPE html> 
>+<meta charset="utf-8">
>+<title>CSS Text Decoration: text-decoration-inset: 0 does not change the decoration</title>
>+<link rel="help" href="https://drafts.csswg.org/css-text-decor-4/#text-decoration-inset-property">
>+<meta name="assert" content="text-decoration-inset: 0 (the initial value) leaves the underline unchanged.">
>+<style>body { margin: 20px; font: 40px/1.5 monospace; }</style>
>+<p><u style="text-decoration-inset: 0">abcdef</u></p>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/html/rendering/widgets/shadow-dom-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/html/rendering/widgets/shadow-dom-expected.txt
>index 44b490fbd3c6..2ce64b1235b1 100644
>--- a/LayoutTests/imported/w3c/web-platform-tests/html/rendering/widgets/shadow-dom-expected.txt
>+++ b/LayoutTests/imported/w3c/web-platform-tests/html/rendering/widgets/shadow-dom-expected.txt
>@@ -1,9 +1,9 @@
> 
> 
>-FAIL <video controls=""></video> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 445
>-FAIL <video></video> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 445
>-FAIL <audio></audio> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 445
>-FAIL <audio controls=""></audio> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 446
>+FAIL <video controls=""></video> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 446
>+FAIL <video></video> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 446
>+FAIL <audio></audio> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 446
>+FAIL <audio controls=""></audio> has a shadow tree with no slots assert_equals: child should be outside the flat tree expected 0 but got 447
> PASS <select></select> has a shadow tree with slot
> PASS <select multiple=""></select> has a shadow tree with slot
> PASS <select size="4"></select> has a shadow tree with slot

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Attachments on bug 319178: 480520 | 480523 | 480524 | 480532 | 480542 | 480554 | 480566 | 480567 | 480579 | 480585 | 480590