A change log between two versions would be enough for me. (e.g. 4.6 -> 4.7). Then I can trace it back to 4.5.
Important is also that the actual API reference keeps up with the changes and does not show obsolete/deprecated calls (Unreal Engine API Reference | Unreal Engine Documentation)
I know it is a long shot for an indie market engine, but I would like to compare to the Mathworks Matlab documentation. They have an example for every command in there. It is frightening, but that’s how it is. It is really helpful.
Sometimes they even go indepth about the actual math if you own a license.
Following a few ‘see also’ commands at the bottom shows even nicer stuff.