Writing to screen by Javascript

The new 508 rules in the US [1] have a new requirement for Javascript: that 
information written to to the page by a script be accessible to a 
screenreader. WCAG 2.0 will need to face a similar question. Here's 
examples the 508 rule gives:

quote
For instance, if a web page uses a script only to fill the contents of an 
HTML form with basic default values, the web page will likely comply with 
this requirement, as the text inserted into the form by the script may be 
readable by a screen reader. By contrast, if a web page uses a script to 
create a graphic map of menu choices when the user moves the pointer over 
an icon, the web site designer may be required to incorporate "redundant 
text links" that match the menu choices because functional text for each 
menu choice cannot be rendered to the assistive technology. Determining 
whether a web page meets this requirement may require careful testing by 
web site designers, particularly as both assistive technology and the 
JavaScript standard continue to evolve.
unquote

This raises questions like:
on the AT&T home page [2] they have mouseovers that swap images and also 
swap the alt text for the images. In principle, a screenreader that 
accesses the DOM will be able to read the new ALT text.  But is the 
screenreader notified when the DOM changes?  and can it access the new alt 
text?

Also, how does the user initiate the mouseover?  In principle, the 
screenreader could simulate a mouseover but does it?

Of course, when I say "screenreader", that's shorthand for
   - an standard browser with an extra screenreader or
   - a speech enabled browser like IBM's home page reader, emacspeak/w3, or 
the late pwWebSpeak.




[1] http://www.access-board.gov/sec508/508standards.htm#SUMMARY
[2] http://www.att.com
--
Leonard R. Kasday, Ph.D.
Institute on Disabilities/UAP and Dept. of Electrical Engineering at Temple 
University
(215) 204-2247 (voice)                 (800) 750-7428 (TTY)
http://astro.temple.edu/~kasday         mailto:kasday@acm.org

Chair, W3C Web Accessibility Initiative Evaluation and Repair Tools Group
http://www.w3.org/WAI/ER/IG/

The WAVE web page accessibility evaluation assistant: 
http://www.temple.edu/inst_disabilities/piat/wave/