Questions regarding performExpiringActivityWithReason: and other activities

Hi,

I need to use background task assertions for an extension. As such, it is recommended to use ProcessInfo's performExpiringActivityWithReason: method.

I've a few questions:

1. Can I call this method as soon as I start performing the work in the foreground, like this is recommended for beginBackgroundTask:expirationHandler: (i.e. even if the extension never moves to the background) or should I call it only as the extension enters the background?
2. Can I have multiple background task assertions like with beginBackgroundTask:expirationHandler: ?
3. Beyond the expiration handler, are there any difference with the other activity methods (beginActivityWithOptions:reason:/endActivity: and performActivityWithOptions:reason:usingBlock:)?
4. In my main app, can I use both UIApplication's beginBackgroundTask:expirationHandler: and ProcessInfo's activity methods (see last question)?
5. Does the activity option NSActivityUserInitiated prevents the app/extension to be suspended as soon as it enters the background, or does it has another use/behavior?
6. What's the difference between sudden termination and automatic termination?
7. Are the flags NSActivitySuddenTerminationDisabled and NSActivityAutomaticTerminationDisabled automatically infered when using the NSActivityBackground or NSActivityUserInitiated options? If not, can I use them together?
8. Which method and flags should I use around file operations?
9. Can I use nested activities? For example (pseudo-code):

beginActivityWithOptions:reason: (or UIApplication's background task for main app)

    performExpiringActivityWithReason: { /*work that should not be interrupted in the middle (e.g. could lead to data corruption)*/ }

    // user-initiated, non-cancellable work that should attempt to complete even after the extension moves to the background.
    // Interrupting this work in the middle has no side-effects like data corruption.

    performExpiringActivityWithReason: { /*work that should not be interrupted in the middle (e.g. could lead to data corruption)*/ }

endActivity:

Thanks.