ACTION-573: Scoping for section 6.4

I propose to add the following text to the introduction of section  
6.4, right before 6.4.1:

> User agents MAY communicate additional indicators to users.  E.g., a  
> user agent could additionally display a persistent indicator in a  
> "danger" situation.

Regards,
--
Thomas Roessler, W3C  <tlr@w3.org>