MDL-48665 a discussion was raised about when customdata in moodleforms should be allowed to be objects or any other structure.
Finally it was agreed that any structure is ok (there are already uses... see the original issue for more details).
So this is about to tidy places where customdata and array are documented together changing them to explicitly say that any structure is allowed. It's up to the developer to consider when an object is ok... or an array maybe needed in case future/dynamic structures are going to be passed or whatever.
A preliminary search returned at least these 2 places to modify: