JSON:API module now supports fetching entity revisions that are not the default revision.
To request a specific entity revision by its ID, use a query parameter like so: ?resourceVersion=id:{revision_id}
When the Content Moderation module is installed and you do not have a known revision ID, you may find it useful to use relative version arguments like so: ?resourceVersion=rel:latest-version or ?resourceVersion=rel:working-copy to get the default revision and the latest revision of an entity, respectively. Without Content Moderation installed, these do not have a meaningful effect.
This change introduces a concept of versions and a working copies. Despite its similar name, a version is not synonymous with a revision. A revision is only determined to be a version if it is or was a default revision. In more familiar language—drafts are not versions. Finally, the latest revision is always known as the working copy since it is the revision to which any editorial work will be done.
These concepts were drawn from RFC 5829 - Link Relation Types for Simple Version Navigation between Web Resources, which heavily influenced the design of this protocol.
More documentation is available here: https://www.drupal.org/docs/8/modules/json-api/revisions
