Ambiguous "should" in an informative section

ARIA uses the normative key word 'should' in an informative section as  
follows:
"The element with focus should not be destroyed, hidden, or scrolled  
off screen."

Please make sure that normative-looking statements aren't made in  
informative sections and please clarify if the sentence is aimed at  
user agents or authors (and what happens if the 'should' is violated).

-- 
Henri Sivonen
hsivonen@iki.fi
http://hsivonen.iki.fi/