[css-contain-3] Tighten up normative definition of inline size containment. w3c#6426

Author: fantasai

css-contain-3/Overview.bs

@@ -83,9 +83,12 @@ Strong Containment: the 'contain' property</h2>
 	<dl dfn-type=value dfn-for=contain>
 		<dt><dfn>inline-size</dfn>
 		<dd>
-			The value turns on <a>inline-size containment</a> for the element.
-			This ensures that the inline [=size containment box|containment box=] can be laid out
-			without needing to examine its descendants.
+			This value turns on [=inline-size containment=] for the element.
+			This prevents the [=inline-size=] of its [=principal box=]
+			from directly depending on its contents.
+
+			Note: There can still be indirect dependencies,
+			see [[#containment-inline-size]].
 	</dl>
 
 
@@ -97,12 +100,20 @@ Types of Containment</h2>
 <h3 id='containment-inline-size'>
 Inline-Size Containment</h3>
 
-	Giving an element <dfn export>inline-size containment</dfn>
-	applies [=size containment=] on the element’s [=inline axis=].
-	That means the [=intrinsic size=] of the [=size containment box=]
-	on the element’s [=inline axis=]
-	is determined as if the element had no content.
-	However, content continues to impact the element’s [=block axis=] [=intrinsic size=].
+	If the element does not generate a <a>principal box</a>
+	(as is the case with ''display: contents'' or ''display: none''),
+	or its [=inner display type=] is ''display/table'',
+	or its [=principal box=] is an <a spec="css-display-3">internal table box</a>,
+	or an <a spec="css-display-3">internal ruby box</a>,
+	or a <a spec="css-display-3" lt="atomic inline">non-atomic</a> <a spec="css-display-3">inline-level</a> box,
+	[=inline-size containment=] has no effect.
+
+	Otherwise, giving an element <dfn export>inline-size containment</dfn>
+	applies [=size containment=] to the [=inline-axis=] sizing of its [=principal box=].
+	This means the [=inline-axis=] [=intrinsic sizes=] of the [=principal box=]
+	are determined as if the element had no content.
+	However, content continues to impact the box’s [=block-axis=] [=intrinsic sizes=] as usual,
+	and the box is allowed to [=fragmentation|fragment=] normally in the [=block axis=].
 
 	<div class=note>
 		In some cases,