[css-nesting-1] Per discussion, & equals :scope in non-nested contexts.

Author: tabatkins

css-nesting-1/Overview.bs

@@ -899,8 +899,8 @@ Nesting Selector: the ''&'' selector {#nest-selector}
 	When used in the selector of a <a>nested style rule</a>,
 	the <a>nesting selector</a> represents the elements matched by the parent rule.
 	When used in any other context,
-	it represents nothing.
-	(That is, it's valid, but matches no elements.)
+	it represents the same elements as '':scope'' in that context
+	(unless otherwise defined).
 
 	<div class="note">
 		The <a>nesting selector</a> can be desugared