code typo http://www.w3.org/TR/wai-aria-practices/

Section 2, step 5, sample code,

The final else clause for other keycodes has
I
(1)     "return return true;"


Also,

(2)  I think it might be more clear if the code said

     if ((event.type == "keydown") || (event.type == "keypress"))

rather than suggesting the cases must be separate.

(3)  var buttonid = getPrevButtonID();  // This is an author defined function

It might help to give a sample implementation in terms of DOM walking.

-jJ