[selectors-4] Update to hypothetical ::shadow w3c#7474

Author: fantasai

selectors-4/Overview.bs

@@ -872,8 +872,8 @@ Internal Structure</h4>
 
 	<div class="example">
 		For example, ''::first-letter + span'' and ''::first-letter em'' are invalid selectors.
-		However, since ''::slotted'' is defined to have internal structure,
-		''::slotted > p'' is a valid selector.
+		However, if ''::shadow'' were defined to have internal structure,
+		''::shadow > p'' would be a valid selector.
 	</div>
 
 	Note: A future specification may expand the capabilities of existing pseudo-elements,