Comment from Stefan

4.2.7.1  Steps for Defining a Logical Navigational Structure

- We have a fundamental issue regarding ARIA roles form and group.

To make it brief, say you have a nested fieldset scenario. You cannot nest two divs with role=form since form derives from HTML concept of form and there nesting of forms is forbidden. If you use role group instead (related concept fieldset according to ARIA spec) you violate ARIA best practices since according to spec group is intended for other purposes. 

And AT? In Jaws landmarks dialog, labelled divs with role=form are perfectly displayed, whereas divs with role=group aren't (since they are no landmarks). 

So bottom line: when you want to use div with role=form  (not role=region!) as nested "fieldset" replacement (which we do since it has great benefit for logical nav structure) make clear in your text that this is perfect, although it violates a base concept from HTML.