Explain that additional private browsing restrictions are not mandated.

Author: mgiuca

index.html

@@ -366,7 +366,8 @@ <h2>
         might leak private data to a third-party application that does not
         respect the user's privacy setting. User agents could present
         additional warnings or disable the feature entirely when in a private
-        browsing mode.
+        browsing mode, but this is not mandated as the chooser UI could be
+        considered sufficient warning.
         </li>
         <li>The data passed to <a><code>navigator.share</code></a> might be
         used to exploit buffer overflow or other remote code execution