[css-cascade-6] Shadowy preludeless scope rule is scoped to host w3c#9178

Author: mirisuzanne

css-cascade-6/Overview.bs

@@ -531,8 +531,11 @@ Identifying Scoping Roots and Limits</h4>
 		If no <<scope-start>> is specified,
 		the [=scoping root=] is the [=parent element=] of the [=owner node=]
 		of the stylesheet where the ''@scope'' rule is defined.
-		(If no such element exists,
-		then the [=scoping root=] is the [=root=] of the containing [=node tree=].)
+		(If no such element exists
+		and the containing [=node tree=] is a [=shadow tree=],
+		then the [=scoping root=] is the [=shadow host=].
+		Otherwise,
+		the [=scoping root=] is the [=root=] of the containing [=node tree=].)
 		Any '':scope'' or ''&'' selectors in <<scope-start>>
 		are interpreted as defined for its outer context.
 
@@ -722,6 +725,10 @@ Changes since the 21 March 2023 Working Draft</h3>
 	Significant changes since the
 	<a href="https://www.w3.org/TR/2023/WD-css-cascade-6-20230321/">21 March 2023 Working Draft</a> include:
 
+	* A ''@scope'' rule without ''<<scope-start>>'' scopes to the
+		[==shadow host==] instead of the [==shadow root==].
+		(<a href="https://github.com/w3c/csswg-drafts/issues/9178">Issue 9178</a>)
+
 	* Clarified that [=scope proximity=] is a single measurement of the steps
 		between a single [=scoping root=] and [=scoped style rule=] [=subject=].