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…a line between two block level boxes
<span style="-webkit-box-decoration-break: clone; border: 20px solid magenta">
a
<div>block</div>
<span></span>
<div>block</div>
c
</span>
The two block level boxes should be right next to each other, the way they are in
Blink. Instead a 20px tall line with a 40px wide magenta border box showed up
between them, for the empty inline box.
The test case is adapted from Oriol Brufau's reduction in
w3c/csswg-drafts#14104
Line::initialize hands a line spanning inline box run the width of its cloned
decoration, so isContentfulOrHasDecoration answered "contentful" on its very first
check (run.logicalWidth()) and the line got a full strut. The fragment's display box
was then built from the border box, so all four cloned edges painted.
Cloned decoration wraps the content of a box fragment, so it can't make a line
contentful by itself. A line spanning inline box start no longer does, and on a line
with no inline content its display box uses the content box -the rule block lines
already followed. This matches Blink.
WebKit-Bug: https://bugs.webkit.org/show_bug.cgi?id=321143
WebKit-Canonical-Link: https://commits.webkit.org/318718@main
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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annevk
enabled auto-merge (rebase)
October 25, 2026 08:55
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WebKit export from bug: [IFC] Inline box with cloned decoration generates an extra line between two block level boxes
[block-in-inline] Inline box with cloned decoration generates an extra line between two block level boxes <span style="-webkit-box-decoration-break: clone; border: 20px solid magenta"> a <div>block</div> <span></span> <div>block</div> c </span> The two block level boxes should be right next to each other, the way they are in Blink. Instead a 20px tall line with a 40px wide magenta border box showed up between them, for the empty inline box. The test case is adapted from Oriol Brufau's reduction in w3c/csswg-drafts#14104 Line::initialize hands a line spanning inline box run the width of its cloned decoration, so isContentfulOrHasDecoration answered "contentful" on its very first check (run.logicalWidth()) and the line got a full strut. The fragment's display box was then built from the border box, so all four cloned edges painted. Cloned decoration wraps the content of a box fragment, so it can't make a line contentful by itself. A line spanning inline box start no longer does, and on a line with no inline content its display box uses the content box -the rule block lines already followed. This matches Blink. WebKit-Bug: https://bugs.webkit.org/show_bug.cgi?id=321143 WebKit-Canonical-Link: https://commits.webkit.org/318718@main Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>