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">.

See Wonder/Examples/Ajax/ERDivaLookExample.

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 the contents of div#a.