[css-overflow-3] Allow single-axis scrollability w3c#12289

Author: fantasai

css-overflow-3/Overview.bs

@@ -235,7 +235,7 @@ Scrolling Overflow</h3>
 	coincides with its padding box,
 	and is called the <dfn export>scrollport</dfn>.
 	A box’s <dfn export>nearest scroll container</dfn>
-	is the its nearest [=scroll container=] ancestor in the [=containing block chain=].
+	is the nearest [=scroll container=] ancestor in the [=containing block chain=].
 	(See [[#overflow-properties]] for control over whether a box clips or scrolls its overflow.)
 
 	Scrolling operations can be initiated by the user
@@ -325,24 +325,24 @@ Clipping and Scrolling Overflow</h2>
 
 	The properties in this chapter specify whether and where a box’s [=overflow=] is clipped;
 	if so, whether it is a [=scroll container=];
-	and if so, in which axis(es) it is allowed to scroll,
+	and if so, in which axis(es) it is allowed to scroll (its <dfn export lt="scrollable axis">scrollable axis(es)</dfn>),
 	thus which of the following types of [=scroll container=] it is:
 
 	<dl>
-		<dt><dfn>single-axis scroll container</dfn>
+		<dt><dfn export>single-axis scroll container</dfn>
 		<dd>
-			A [=scroll container=] that can scroll in only one axis.
+			A [=scroll container=] that is scrollable in only one axis.
 
-		<dt><dfn>dual-axis scroll container</dfn>
+		<dt><dfn export>dual-axis scroll container</dfn>
 		<dd>
-			A [=scroll container=] that can scroll in both axes.
+			A [=scroll container=] that is scrollable in both axes.
 
-		<dt><dfn>block-axis scroll container</dfn>
-		<dt><dfn>inline-axis scroll container</dfn>
-		<dt><dfn>x-axis scroll container</dfn>
-		<dt><dfn>y-axis scroll container</dfn>
+		<dt><dfn export>block-axis scroll container</dfn>
+		<dt><dfn export>inline-axis scroll container</dfn>
+		<dt><dfn export>x-axis scroll container</dfn>
+		<dt><dfn export>y-axis scroll container</dfn>
 		<dd>
-			A [=scroll container=] that can scroll in the specified axis,
+			A [=scroll container=] that is scrollable in the specified axis,
 			regardless of whether it can also scroll in the other axis.
 	</dl>
 
@@ -398,7 +398,6 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 		<dd>
 			There is no special handling of overflow, that is,
 			the box’s content is rendered outside the box if positioned there.
-			The box is not a <a>scroll container</a>.
 
 		<dt><dfn>hidden</dfn>
 		<dd>
@@ -410,8 +409,7 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 			such as dragging on a touch screen
 			or using the scrolling wheel on a mouse.
 			However, the content must still be scrollable programmatically,
-			for example using the mechanisms defined in [[CSSOM-VIEW]],
-			and the box is therefore still a <a>scroll container</a>.
+			for example using the mechanisms defined in [[CSSOM-VIEW]].
 
 		<dt><dfn>clip</dfn>
 		<dd>
@@ -422,8 +420,7 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 			In addition, unlike ''overflow: hidden''
 			which still allows programmatic scrolling,
 			''overflow: clip'' forbids scrolling entirely,
-			through any mechanism,
-			and therefore the box is not a <a>scroll container</a>.
+			through any mechanism.
 
 			Unlike ''hidden'', this value <strong>does not</strong> cause
 			the element to establish a new formatting context.
@@ -435,8 +432,8 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 		<dd>
 			This value indicates that
 			the content is clipped to the [=overflow clip edge=],
-			but can be scrolled into view
-			(and therefore the box is a <a>scroll container</a>).
+			but can be scrolled into view.
+
 			Furthermore, if the user agent uses a scrolling mechanism
 			that is visible on the screen (such as a scroll bar or a panner),
 			that mechanism should be displayed
@@ -458,21 +455,28 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 	</dl>
 
 	The ''overflow/scroll'', ''overflow/auto'', and ''overflow/hidden'' values
-	are known as the <dfn export lt="scrollable overflow value">scrollable values</dfn> of 'overflow'.
+	are known as the <dfn export lt="scrollable overflow value" local-lt="scrollable value">scrollable values</dfn> of 'overflow'.
+	They cause the box to be a [=scroll container=]
+	and the affected axis to be a [=scrollable axis=].
+	A [=block box=] that becomes a [=scroll container=]
+	also establishes an [=independent formatting context=].
+
 	The  ''overflow/visible'' and ''overflow/clip'' values
 	are known as the <dfn export lt="non-scrollable overflow value">non-scrollable values</dfn>.
+	However, if the other axis specifies a [=scrollable value=],
+	a specified value of  ''visible''
+	[=computed value|computes=] to ''overflow/auto'',
+	enabling scrolling in its axis.
+	If neither axis computes to a [=scrollable value=],
+	the box is not a [=scroll container=].
+	If only one axis computes to a [=scrollable value=]
+	(i.e. the other axis is ''overflow/clip''),
+	the box is a [=single-axis scroll container=].
 
-	The  ''visible''/''overflow/clip'' values of 'overflow'
-	compute to ''overflow/auto''/''hidden'' (respectively)
-	if one of 'overflow-x' or 'overflow-y' is neither ''visible'' nor ''overflow/clip''.
 	On [=replaced elements=],
 	a [=computed value|computed=] ''overflow/hidden'' value further resolves
 	to a [=used value=] of ''overflow/clip''.
 
-	If the computed value of 'overflow' on a <a>block box</a>
-	is neither ''overflow/visible'' nor ''overflow/clip'' nor a combination thereof,
-	it [=establishes an independent formatting context=] for its contents.
-
 	User agents must also support
 	the <dfn value for="overflow, overflow-x, overflow-y, overflow-block, overflow-inline">overlay</dfn> keyword
 	as a [=legacy value alias=] of ''overflow/auto''.
@@ -1334,6 +1338,11 @@ ellipsis interaction with scrolling interfaces</h4>
 
 	This appendix is <em>informative</em>.
 
+	Significant changes since the <a href="https://www.w3.org/TR/2025/WD-css-overflow-3-20251007/">7 October 2025 Working Draft</a>:
+	* Allow combining ''overflow: clip'' behavior in one axis with scrolling in the other,
+		to allow single-axis trapping for e.g. [=sticky positioning=].
+		(<a href="https://github.com/w3c/csswg-drafts/issues/12289">Issue 12289</a>)
+
 	Significant changes since the <a href="https://www.w3.org/TR/2023/WD-css-overflow-3-20230329/">29 March 2023 Working Draft</a>:
 
 	* Define that ''overflow: hidden'' is treated as ''overflow: clip'' on [=replaced elements=].