In some cases the documentation just plain wrong. Core data can be confusing, but worse with wrong documentation. I've had an open radar about the merge policy documentation for over 3 years and nothing has happened, even after talking to a core data engineer at WWDC in 2018.

These two should be the same, but see the conflicting description: https://developer.apple.com/documentation/coredata/nsmergepo... (in-memory changes trump) https://developer.apple.com/documentation/coredata/nsmergeby... (external changes trump)

Same here: https://developer.apple.com/documentation/coredata/nsmergepo... (external changes trump) https://developer.apple.com/documentation/coredata/nsmergeby... (in-memory changes trump)