ARIA best practice doc: new dimension to role=alert

In section "5.3. Choosing Between Special Case Live Regions", the alert role  is assigned an added meaning: "one-time notification which shows for a period of time and goes away".  ... 'goes away' appears to convey 'go away automatically ... without user action' i.e. say after 10 seconds or 30 seconds or the like.  
(See http://www.w3.org/WAI/PF/aria-practices/#chobet).

I do not see anything  to this effect being suggested in the normative doc that explains role=alert.
See http://www.w3.org/TR/wai-aria/roles#alert
I hope this is not how 'time sensitive' is being interpreted by the authoring practice doc?

Thanks,
Sailesh Panchang

Received on Friday, 13 December 2013 20:51:15 UTC