There was a section in the talk about how we can break down migration into smaller changes, and that we have an opportunity to run app-specific code in between migration steps. However the talk didn't touch on how can can achieve this, besides a single sentence, which doesn't give enough detail at least for me to figure out how to do it. Intuitively, an event loop could be built that opens the persistent store with the lightweight migration options set and iteratively steps through each unprocessed model in a serial order, and Core Data will migrate the store. Given the automatic nature of the lightweight migrations, especially in the case where we're using NSPersistentCoordinator, doesn't the automatic system just zoom through all of the migrations from model A --> A' --> A'' -> B? How to we make it stop so we can execute our own app code? Thanks!