[selectors-4] Disallow nesting :has() inside :has(). #6952

Author: byung-woo

selectors-4/Overview.bs

@@ -1194,6 +1194,8 @@ The Relational Pseudo-class: '':has()''
 	would match at least one element
 	when [=anchor element|anchored against=] this element.
 
+	'':has()'' pseudo-class cannot be nested; '':has()'' is not valid within '':has()''.
+
 
 		For example, the following selector matches only
 		<a> elements that contain an <img> child: