[css-cascade-6] Clarify that style rules within name-defining rules are still scoped.

Author: fantasai

css-cascade-6/Overview.bs

@@ -517,6 +517,9 @@ Scope Nesting</h4>
 	that are defined inside ''@scope'' are valid,
 	but are not scoped or otherwise affected
 	by the enclosing ''@scope'' rule.
+	However, any [=style rules=] contained by such rules
+	(e.g. within ''@layer'')
+	are [=scoped style rules|scoped=].
 
 <h3 id="scope-combinator">
 Scoped Descendant Combinator</h3>