I’ve updated with a couple of links. A lot is not concrete though, so would be a mix of the safe-primer, and forum reading.
Eg, I dont think we’ve a concrete explanation or RFC for the ‘containers’ idea. But the general background was that there was preiviously a fixed set of mutable data, ‘containers’ (for photos, documents, eg), in the accounts root. And that apps could request permission to store things in these, but otherwise there was no method of sharing/discovering data between apps. Apps also had their own, exclusive, unshareable container too.
Hope that helps @loziniak, any more Qs just shout and I’ll do my best to answer 