Currently, diffs are not displayed particularly well, especially when it comes to arrays (e.g. identifiers): https://beta.bookbrainz.org/revision/13319

The library currently used for diffs does not handle arrays of objects. Instead we can use jsondiffpatch which works quite well, including with arrays of objects.
(Considering jsondiffpatch does not seem very active, if you have a better suggestion, please do test it)

Diffs are calculated in the ORM package and used in the webserver where the diff formatters will require a significant rewrite to adapt to the new delta format