Name: column-rule-inset-cap-start, column-rule-inset-cap-end, column-rule-inset-junction-start, column-rule-inset-junction-end, row-rule-inset-cap-start, row-rule-inset-cap-end, row-rule-inset-junction-start, row-rule-inset-junction-end
-		Value: <>
+		Value: <> | ''overlap-join''
 		Initial: ''0''
 		Applies to: grid containers, flex containers, multicol containers, and grid lanes containers
 		Inherited: no
@@ -1097,6 +1097,65 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 		For these properties, positive values offset in the [=start=] direction, and negative values offset in the [=end=] direction, along the axis of the gap.
 	

 
+	

+		The overlap-join keyword
+		produces neat joins between crossing [=gap decorations=]:
+	
+
+	

+		

+			At a [=junction segment endpoint=], the [=gap decoration=] extends across the [=gap junction=]
+			far enough to overlap the crossing decoration.
+
+			

+				Note: At a [=junction segment endpoint=], this is equivalent to an inset of
+				''calc(-50% - w / 2)'',
+				where w is the [=used value=] of the crossing decoration's
+				'column-rule-width' or 'row-rule-width'.
+			
+		

+			At a [=cap segment endpoint=], it has no effect; the [=gap decoration=] ends at the [=segment endpoint=].
+	
+
+	

+		
+			.inset-overlap-join {
+				rule-inset: overlap-join;
+				rule-break: intersection;
+				rule-visibility-items: between;
+			}
+		
+		

+			
+		
+		
+	
+
+	

+		
+			.inset-overlap-join {
+				rule-inset: overlap-join;
+				rule-break: intersection;
+				rule-visibility-items: between;
+			}
+		
+		

+			
+		
+		
+	
+
 	

 		
 			.inset-end {
@@ -1159,6 +1218,13 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 		multicol/multicol-gap-decorations-022.html
 		multicol/multicol-gap-decorations-023.html
 		multicol/multicol-gap-decorations-033.html
+		parsing/rule-inset-cap-start-end-overlap-join-computed.html
+		parsing/rule-inset-cap-start-end-overlap-join-invalid.html
+		parsing/rule-inset-junction-start-end-overlap-join-computed.html
+		parsing/rule-inset-junction-start-end-overlap-join-invalid.html
+		grid/grid-gap-decorations-overlap-join-001.html
+		grid/grid-gap-decorations-overlap-join-002.html
+		grid/grid-gap-decorations-overlap-join-dangling-001.html
 	
 
 	

@@ -1184,7 +1250,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 
 	
 		Name: column-rule-inset-start, column-rule-inset-end, row-rule-inset-start, row-rule-inset-end
-		Value: <>
+		Value: <> | ''overlap-join''
 		Applies to: Same as 'column-rule-inset-cap-start', 'column-rule-inset-junction-start', 'column-rule-inset-cap-end', 'column-rule-inset-junction-end', 'row-rule-inset-cap-start', 'row-rule-inset-junction-start', 'row-rule-inset-cap-end', and 'row-rule-inset-junction-end'
 	
 
@@ -1240,7 +1306,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 
 	
 		Name: column-rule-inset-cap, column-rule-inset-junction, row-rule-inset-cap, row-rule-inset-junction
-		Value: <> [ <> ]?
+		Value: [ <> | ''overlap-join'' ] [ <> | ''overlap-join'' ]?
 		Applies to: Same as 'column-rule-inset-cap-start', 'column-rule-inset-cap-end', 'column-rule-inset-junction-start', 'column-rule-inset-junction-end', 'row-rule-inset-cap-start', 'row-rule-inset-cap-end', 'row-rule-inset-junction-start', and 'row-rule-inset-junction-end'
 	
 
@@ -2572,6 +2638,8 @@ Changes since the 2
 			(Issue 13697)
 		
Clarified that gaps suppressed due to fragmentation still consume gap decoration values.
 			(Issue 13754)
+		
Added the ''overlap-join'' value to the [[#inset|rule-inset]] properties.
+			(Issue 13137)
 	
 
 

diff --git a/css-gaps-1/images/example-1-overlap-join.png b/css-gaps-1/images/example-1-overlap-join.png
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Date: Mon, 27 Apr 2026 20:07:54 -0700
Subject: [PATCH 2/9] nit and update

---
 css-gaps-1/Overview.bs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs
index 99ee4a183af6..9e4f1f4e4d3a 100644
--- a/css-gaps-1/Overview.bs
+++ b/css-gaps-1/Overview.bs
@@ -1111,7 +1111,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 				Note: At a [=junction segment endpoint=], this is equivalent to an inset of
 				''calc(-50% - w / 2)'',
 				where w is the [=used value=] of the crossing decoration's
-				'column-rule-width' or 'row-rule-width'.
+				'column-rule-width' or 'row-rule-width', whichever applies.
 			

 		

 			At a [=cap segment endpoint=], it has no effect; the [=gap decoration=] ends at the [=segment endpoint=].
@@ -1130,7 +1130,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 		
 		
@@ -1147,8 +1147,8 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 		

 			
 		
 		

-			
+			
 		
 		
 	
@@ -1145,13 +1146,14 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 			}
 		

- +

Date: Wed, 29 Apr 2026 13:21:21 -0700 Subject: [PATCH 4/9] nit --- css-gaps-1/Overview.bs | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index c72b0d7144a3..270a40fd8768 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -1099,13 +1099,14 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

The overlap-join keyword - produces neat joins between crossing [=gap decorations=]: + produces neat joins between [=gap decorations=] that meet at the same [=gap junction=]:

• - At a [=junction segment endpoint=], the [=gap decoration=] extends across the [=gap junction=] - far enough to overlap the crossing decoration. + At a [=junction segment endpoint=], the [=gap decoration=] extends into the [=gap junction=] + by half the [=crossing gap width=], plus half the [=used value=] of the crossing decoration's + 'column-rule-width' or 'row-rule-width' (whichever applies).

  Note: At a [=junction segment endpoint=], this is equivalent to an inset of @@ -1115,7 +1116,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

• At a [=cap segment endpoint=], it computes to ''0''; the [=gap decoration=] remains flush - at the [=segment endpoint=]. + at the [=segment endpoint=], because there is no other segment to join with.

@@ -1130,8 +1131,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties @@ -1151,9 +1151,8 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties In a "donut" grid layout, where items surround an empty space in the middle of the container, ''overlap-join'' joins adjacent segments at the [=junction segment endpoints=], - extending each [=gap decoration=] across the [=gap junction=] to overlap the crossing decoration. - At the [=cap segment endpoints=] bordering the empty interior region, - ''overlap-join'' computes to ''0''. + extending each [=gap decoration=] into the [=gap junction=]. At the [=cap segment endpoints=] + bordering the edge of the container and the empty interior region, ''overlap-join'' computes to ''0''.

From 71e938c0735c4aae34041250cbadae99267daf4a Mon Sep 17 00:00:00 2001 From: "Sam Davis Omekara (from Dev Box)" Date: Wed, 29 Apr 2026 16:43:50 -0700 Subject: [PATCH 5/9] prod + inset-value --- css-gaps-1/Overview.bs | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index 270a40fd8768..b5ae6d763f44 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -983,7 +983,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

 		Name: column-rule-inset-cap-start, column-rule-inset-cap-end, column-rule-inset-junction-start, column-rule-inset-junction-end, row-rule-inset-cap-start, row-rule-inset-cap-end, row-rule-inset-junction-start, row-rule-inset-junction-end
-		Value: <> | ''overlap-join''
+		Value: <>
 		Initial: ''0''
 		Applies to: grid containers, flex containers, multicol containers, and grid lanes containers
 		Inherited: no
@@ -991,6 +991,10 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties
 		Animation type: by computed value type
 	

+

+		<inset-value> = <> | overlap-join
+	

+ These properties can be used to offset the start and end points of gap decorations relative to the segment endpoints which would normally determine where decorations start and end. @@ -1098,7 +1102,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

- The overlap-join keyword + The overlap-join keyword produces neat joins between [=gap decorations=] that meet at the same [=gap junction=]:

@@ -1130,9 +1134,9 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

@@ -1149,10 +1153,10 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties @@ -1251,7 +1255,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

 		Name: column-rule-inset-start, column-rule-inset-end, row-rule-inset-start, row-rule-inset-end
-		Value: <> | ''overlap-join''
+		Value: <>
 		Applies to: Same as 'column-rule-inset-cap-start', 'column-rule-inset-junction-start', 'column-rule-inset-cap-end', 'column-rule-inset-junction-end', 'row-rule-inset-cap-start', 'row-rule-inset-junction-start', 'row-rule-inset-cap-end', and 'row-rule-inset-junction-end'
 	

@@ -1307,7 +1311,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

 		Name: column-rule-inset-cap, column-rule-inset-junction, row-rule-inset-cap, row-rule-inset-junction
-		Value: [ <> | ''overlap-join'' ] [ <> | ''overlap-join'' ]?
+		Value: <> <>?
 		Applies to: Same as 'column-rule-inset-cap-start', 'column-rule-inset-cap-end', 'column-rule-inset-junction-start', 'column-rule-inset-junction-end', 'row-rule-inset-cap-start', 'row-rule-inset-cap-end', 'row-rule-inset-junction-start', and 'row-rule-inset-junction-end'
 	

@@ -2639,7 +2643,7 @@ Changes since the 2 (Issue 13697)

Clarified that gaps suppressed due to fragmentation still consume gap decoration values. (Issue 13754) -

Added the ''overlap-join'' value to the [[#inset|rule-inset]] properties. +

Added the ''/overlap-join'' value to the [[#inset|rule-inset]] properties. (Issue 13137) From 21e86502de9620495f46a222c9ccc60127347fc5 Mon Sep 17 00:00:00 2001 From: Sam Davis <59079555+oSamDavis@users.noreply.github.com> Date: Mon, 11 May 2026 09:57:31 -0700 Subject: [PATCH 6/9] Apply suggestions from code review Co-authored-by: Kevin Babbitt --- css-gaps-1/Overview.bs | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index b5ae6d763f44..3bc595ecd8d2 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -1109,7 +1109,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

• At a [=junction segment endpoint=], the [=gap decoration=] extends into the [=gap junction=] - by half the [=crossing gap width=], plus half the [=used value=] of the crossing decoration's + by half the [=crossing gap width=], plus half the [=used value=] of the crossing gap's 'column-rule-width' or 'row-rule-width' (whichever applies).

  @@ -1119,8 +1119,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties 'column-rule-width' or 'row-rule-width', whichever applies.

• - At a [=cap segment endpoint=], it computes to ''0''; the [=gap decoration=] remains flush - at the [=segment endpoint=], because there is no other segment to join with. + At a [=cap segment endpoint=], [=overlap-join=] is treated as ''0''.

@@ -1136,7 +1135,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties

@@ -1156,7 +1155,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties ''/overlap-join'' joins adjacent segments at the [=junction segment endpoints=], extending each [=gap decoration=] into the [=gap junction=]. At the [=cap segment endpoints=] - bordering the edge of the container and the empty interior region, ''/overlap-join'' computes to ''0''. + bordering the edge of the container and the empty interior region, ''/overlap-join'' is treated as ''0''. From 97139854c01c66e5538057e2cf1fd263fafeaaf9 Mon Sep 17 00:00:00 2001 From: "Sam Davis Omekara (from Dev Box)" Date: Mon, 11 May 2026 10:53:52 -0700 Subject: [PATCH 7/9] take note out --- css-gaps-1/Overview.bs | 9 --------- 1 file changed, 9 deletions(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index fc271b012a97..104f2b59bc0c 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -1081,15 +1081,6 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties The [=crossing gap width=] is ''0''. -

- Note: This classification by position is distinct from the - [=cap segment endpoint=] / [=junction segment endpoint=] classification. - A [=cap segment endpoint=] may sit at a container edge or at a [=gap junction=] - (see this example). Hence, - ''column-rule-inset-cap-start: 50%'' resolves to half the [=gap junction=] - size at an interior cap and ''0'' at other caps such as container edges. -

-

The 'column-rule-inset-cap-start' and 'row-rule-inset-cap-start' properties apply to [=start segment endpoints=] that are [=cap segment endpoints=]. The 'column-rule-inset-junction-start' and 'row-rule-inset-junction-start' properties apply to [=start segment endpoints=] that are [=junction segment endpoints=]. From da72bd28492b4bed84cd0fd7cca33f0a9903755c Mon Sep 17 00:00:00 2001 From: "Sam Davis Omekara (from Dev Box)" Date: Mon, 11 May 2026 12:37:59 -0700 Subject: [PATCH 8/9] nit --- css-gaps-1/Overview.bs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index 104f2b59bc0c..36e4ab0e3ca7 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -1110,7 +1110,7 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties 'column-rule-width' or 'row-rule-width', whichever applies.

- At a [=cap segment endpoint=], [=overlap-join=] is treated as ''0''. + At a [=cap segment endpoint=], ''/overlap-join'' is treated as ''0''.

From a8092c87de9413334cec097b6a0c6542059b0d9e Mon Sep 17 00:00:00 2001 From: "Sam Davis Omekara (from Dev Box)" Date: Mon, 11 May 2026 12:41:48 -0700 Subject: [PATCH 9/9] nit note --- css-gaps-1/Overview.bs | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/css-gaps-1/Overview.bs b/css-gaps-1/Overview.bs index 36e4ab0e3ca7..8796eee04673 100644 --- a/css-gaps-1/Overview.bs +++ b/css-gaps-1/Overview.bs @@ -1081,6 +1081,15 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties The [=crossing gap width=] is ''0''. +

+ Note: This classification by position is distinct from the + [=cap segment endpoint=] / [=junction segment endpoint=] classification. + A [=cap segment endpoint=] may sit at a container edge or at a [=gap junction=] + (see this example). Hence, + ''column-rule-inset-cap-start: 50%'' resolves to half the [=gap junction=] + size at an interior cap and ''0'' at other caps such as container edges. +

+

The 'column-rule-inset-cap-start' and 'row-rule-inset-cap-start' properties apply to [=start segment endpoints=] that are [=cap segment endpoints=]. The 'column-rule-inset-junction-start' and 'row-rule-inset-junction-start' properties apply to [=start segment endpoints=] that are [=junction segment endpoints=]. @@ -1102,13 +1111,6 @@ Adjusting gap decoration endpoints: The 'rule-inset' properties At a [=junction segment endpoint=], the [=gap decoration=] extends into the [=gap junction=] by half the [=crossing gap width=], plus half the [=used value=] of the crossing gap's 'column-rule-width' or 'row-rule-width' (whichever applies). - -

- Note: At a [=junction segment endpoint=], this is equivalent to an inset of - ''calc(-50% - |w| / 2)'', - where |w| is the [=used value=] of the crossing decoration's - 'column-rule-width' or 'row-rule-width', whichever applies. -

At a [=cap segment endpoint=], ''/overlap-join'' is treated as ''0''.