[selectors-4] :nth-child() and :nth-last-child() also use forgiving-selector parsing, per original resolution. w3c#3264

Author: fantasai

selectors-4/Overview.bs

@@ -2817,7 +2817,8 @@ Child-indexed Pseudo-classes</h3>
 	pseudo-class notation represents elements that
 	are among <var>An+B</var>th elements
 	from the list composed of
-	their <a>inclusive siblings</a> that match the <a>selector list</a> <var>S</var>.
+	their <a>inclusive siblings</a> that match the <a>selector list</a> <var>S</var>,
+	which is [=parsed as a forgiving selector list=].
 	If <var>S</var> is omitted,
 	it defaults to ''*|*''.
 
@@ -2914,6 +2915,7 @@ Child-indexed Pseudo-classes</h3>
 	from the list composed of
 	their <a>inclusive siblings</a> that match the <a>selector list</a> <var>S</var>,
 	counting backwards from the end.
+	<var>S</var> is [=parsed as a forgiving selector list=].
 	If <var>S</var> is omitted,
 	it defaults to ''*|*''.