How I understand things, a display region is a dynamic part of a
webpage;
Depending on the place you're at, a display region is populated with a
specific activity.
A activity manager is the manager of a display region and decides the
right activity to show up for a given display region when a certain
page is showing.
So, in terms of your question : a display region can be a dynamic
menu, a sidebar, a logout/login link.... not the entire group.
An example
page with menu displayregion, maincontent displayregion, sidebar
displayregion
example page #ContactDetailsPage:FooBar
+> sidebar display region will be instructed by the sidebar-
activitymanager to start the activity GrandChildrenActivity (display
grandchildren in side bar)
+> maincontact display region will be instructed by the
maincontentarea-activitymanager to start the activity
ContactDetailsActivity (display contact details in main content area)
+> menu display region will be instructed by the menu-activitymanager
to start the activity MenuActivity (show the menu)
example page #Login
+> sidebar display region will be instructed by the sidebar-
activitymanager to display nothing (NULL)
+> maincontact display region will be instructed by the
maincontentarea-activitymanager to start the activity LoginActivity
(display login page)
+> menu display region will be instructed by the menu-activitymanager
to start the activity WelcomeActivity (show a welcome msg)
etc etc.