Refinements documentation is based on older implementation
It seems that the refinements documentation hasn't been updated to reflect more recent changes to how refinements work. For example, [[https://github.com/ruby/ruby/blob/trunk/doc/syntax/refinements.rdoc#scope]] says "You may only activate refinements at top-level, not inside any class, module or method scope", whereas the current implementation allows activating refinements anywhere except inside methods.
I've attached one potential reworking to be more accurate, but I don't mind if it's used or not. The main thing is for it to be made correct.