I posted this deep inside another thread, but new users--and the person in charge of writing the help files could probably benefit from this, so I thought I'd try it in a separate thread. (Maybe this can get pinned?)
The graphically inclined could possible construct an illustration. I started to, and concluded I was not sufficiently graphically inclined.
1. The app starts with a Splash Activity that does *not* get placed onto the back stack. (Pressing back will *not* take you back into the Splash Activity.)
2. After Splash closes the app starts into one of three main co-Activities (I think I just invented the term co-Activities), whichever, if any, were last left open when the app was exited:
A. Single Pane View
B. Dual Pane View (panes arranged vertically)
C. Dual Pane View (panes arranged horizontally)
Now, these co-Activities work a bit differently than normal Activities might otherwise flow. That is, one can go from A, to B, then C, but then one does *not* hit back for B, then back for A, then back again to exit the app. Essentially, while they are programmatically separate Activities as far as Android is concerned, they function as co-Activity 'modes' behaving as if they were one single Activity. Moving from any one of these three to another does *not* put or remove activities from the back-stack of activities within the app.
(The reason for this is (hopefully) intuitive. If I like doing dual pane work, I don't want to have to go back through a back stack including the single pane view to exit the app, and when I restart, I want to be back in my dual pane view--not needing to navigate back into it.)
When you are merely viewing a co-Activity (A, B, C) with no dialogs floating about (see #3), pressing the back button will exit the app.
3. The co-Activities allow various dialogs to show, leaving A, B, or C (at least partly) visible underneath. The dialogs can be dismissed either by the back button or tapping outside the dialog (soft-dismiss).
4. The co-Activities do allow the launch of true Activities (not co-Activities) that *do* put the co-Activity into the back stack. These include Library (but see #5), Easy Install, Settings, Help (such as it is at the moment), About and (for now) Diagnostics.
5. The Library has a unique behavior involving the back stack. To exit the Library without making a selection, press the back button and the Library will be removed from the back stack and you will be returned to your A, B, or C co-Activity. BUT, selecting content from the Library will both close the Library (removing it from the back stack), and *replace* whatever co-Activity (A, B or C) with a single pane (A) co-Activity at the top of the back stack. Pressing back after making a Library choice exits the app. It does *not* cycle back through a back-stack of any prior Library selections or prior co-Activities.
It remains to be seen how this will evolve over time, but that is a basic overview of the structure and flow of the app.