Explicitly ban file, javascript, wss, local scheme

Author: marcoscaceres

index.html

@@ -451,6 +451,9 @@ <h3>
                 </li>
                 <li>If |url| is failure, return false.
                 </li>
+                <li>If the |url|'s [=URL/scheme=] is a [=local scheme=], or
+                `file`, or `javascript`, or `wss`, return false.
+                </li>
                 <li>If |url|'s [=URL/scheme=] is not a [=sharable scheme=],
                 return false.
                 </li>