Merge pull request w3c#6378 from andruud/cq_element

[css-contain-3] Make the query container an element, ++

Author: mirisuzanne

css-contain-3/Overview.bs

@@ -25,6 +25,7 @@ spec:css-break-3; type:dfn; text:fragmentation
 spec:css-break-3; type:dfn; text:fragmentation container
 spec:css-break-3; type:dfn; text:fragmentation context
 spec:css-break-3; type:dfn; text:fragmented flow
+spec:css-contain-2; type:dfn; text:layout containment box
 spec:css-sizing-4; type:property; text:contain-intrinsic-size
 spec:css-sizing-4; type:property; text:aspect-ratio
 spec:intersection-observer; type:dfn; text:intersection root
@@ -169,11 +170,11 @@ Creating Query Containers: the 'container-type' property</h2>
 		Initial: none
 		Inherited: no
 		Applies to: all elements
-		Computed value: the keyword ''container-type/none'' or one or more of ''container-type/size'', ''container-type/inline-size'', ''container-type/style'', ''container-type/state''
+		Computed value: the keyword ''container-type/none'' or one or more of ''container-type/size'', ''container-type/inline-size'', ''container-type/block-size'', ''container-type/style'', ''container-type/state''
 		Animation type: not animatable
 	</pre>
 
-	The 'container-type' property establishes the [=principal box=]
+	The 'container-type' property establishes the element
 	as a <dfn export>query container</dfn> for the purpose of [=container queries=],
 	allowing [=style rules=] styling its descendants
 	to query various aspects of its sizing, layout, and style
@@ -192,23 +193,23 @@ Creating Query Containers: the 'container-type' property</h2>
 			Applies [=layout containment=],
 			[=style containment=],
 			and [=size containment=]
-			to this box.
+			the [=principal box=].
 		<dt><dfn>inline-size</dfn>
 		<dd>
 			Establishes a [=query container=] for [=dimensional queries=]
 			on the container’s own [=inline axis=].
 			Applies [=layout containment=],
 			[=style containment=],
 			and [=inline-size containment=]
-			to this box.
+			the [=principal box=].
 		<dt><dfn>block-size</dfn>
 		<dd>
 			Establishes a [=query container=] for [=dimensional queries=]
 			on the container’s own [=block axis=].
 			Applies [=layout containment=],
 			[=style containment=],
 			and [=block-size containment=]
-			to this box.
+			the [=principal box=].
 		<dt><dfn>style</dfn>
 		<dd>
 			Establishes a [=query container=] for [=style queries=].
@@ -274,8 +275,7 @@ Naming Query Containers: the 'container-name' property</h2>
 	</pre>
 
 	The 'container-name' property
-	specifies a list of <dfn export lt="query container name">query container names</dfn>
-	that apply to the box if it is a [=query container=].
+	specifies a list of <dfn export lt="query container name">query container names</dfn>.
 	These names can be used by ''@container'' rules
 	to filter which [=query containers=] are targeted.
 
@@ -431,13 +431,19 @@ Container Features</h2>
 Dimensional Container Features</h3>
 
 	<dfn export>Dimensional queries</dfn> allow querying
-	the size of the [=query container=].
+	the size of the [=query container=]'s [=principal box=].
+
+	If the [=query container=] does not have a [=principal box=],
+	or the principal box is not a [=layout containment box=],
+	then the result of evaluating any dimensional container feature is "unknown".
 
 	[=Relative length=] units in [=container queries=]
-	are based on the the [=computed values=] of the [=query container=] element.
+	are based on the the [=computed values=] of the [=query container=].
 
 	Note: This is different from the handling of relative units in [=media queries=].
 
+	Issue: Evaluate to "unknown" if inline-/block-/size containment is missing.
+
 <h4 id="width">
 Width: the '@container/width' feature</h4>
 
@@ -547,7 +553,7 @@ Orientation: the '@container/orientation' feature</h4>
 Style Container Features</h3>
 
 	<dfn export>Style queries</dfn> allow querying
-	the [=computed values=] of the [=query container=] element.
+	the [=computed values=] of the [=query container=].
 
 	Issue(5989): "container width" and "container height" units