div#a - 'a' is for 'Ajax'
The D2W page content is contained inside div#a.
This is the only pre-requisite of the PageWrapper in a Diva look D2W app: that it places its contents inside a <div id="a">.
div#a - the Primary Ajax Update Container
In a Diva D2W app, div#a is the primary update container.
Here, ajax page configurations like AjaxQueryMovie will update div#a.