[css-conditional-3] ns in supports() invalid, #3220

Author: svgeesus

css-conditional-3/Overview.bs

@@ -680,6 +680,10 @@ partial namespace CSS {
       3. Otherwise, return <code>false</code>.
 
     </div>
+
+    All namespaces in the <var>conditionText</var> argument
+    are considered invalid,
+    just as they are in <var>document.querySelector("a|b")</var>.
 </dl>
 
 <h2 class=no-num id=priv-sec>Privacy and Security Considerations</h2>