https://musicbrainz.org/relationship/a3005666-a872-32c3-ad06-98af558e99b0 says that this relationship supports several attributes, such as "cover" and "instrumental". Given we now have documentation pages for the attributes themselves (e.g. https://musicbrainz.org/relationship-attribute/1e8536bd-6eda-3822-8e78-1c0f4d3d2113), it would be sensible to link to those pages from here. They do not have a ton of info, to be fair, but at the very least they do have the MBID (and the list of other relationships using the same attribute might also be useful).