Example Query:

• XML search: https://beta.musicbrainz.org/ws/2/release-group/?query=rgid:b0d0fc64-11f8-36d3-89bc-e4327c5a6fba
• JSON search: https://beta.musicbrainz.org/ws/2/release-group/?query=rgid:b0d0fc64-11f8-36d3-89bc-e4327c5a6fba&fmt=json
• JSON lookup: https://beta.musicbrainz.org/ws/2/release-group/b0d0fc64-11f8-36d3-89bc-e4327c5a6fba?fmt=json&inc=releases

The attributes 'type' and 'type-id' are old mappings for when we did not have separate primary and secondary types. (These two types are just missing IDs at the moment, see SEARCH-628 and SEARCH-629.) These attributes seem to match the first secondary type if one is set, or the primary type if not. They are marked as optional in our RelaxNG schema, thus can be safely removed.