Visual aid time! So everyone uses the same terms, here is the page from the install book:
Wall cover with back panel attached:
Back panel detached from wall cover, with a close-up of the pinch points that hold them together:
Thermostat with back panel, detached from wall cover. It can be mounted like this if the wall cover is not desired or spouse approved.
Or can be mounted with the wall cover included:
This was a pre-order production unit, looking forward to see if yours differs from this.