does update merge replace the given keys or merge it(arr, set,...)?

[ManReadApp]

MERGE clause

Instead of specifying the full record data using the SET clause or the CONTENT keyword, it is also possible to merge-update only specific fields by using the MERGE keyword and specifying only the fields which are to be updated.

This are the docs to the merge clause. it says which are to be updated. this is not clear how it behaves for arrays/sets/maps. I assume that it means which are to be replaced, but should that be changed to updated => merged/replaced and can I get verification?