+ * Contains the following fields:
+ * - oldRevision (RevisionRecord|null): the revision that was current before the change
+ * associated with this update. Might not be set, use getOldRevision() instead of direct
+ * access.
+ * - oldId (int|null): the id of the above revision. 0 if there is no such revision (the change
+ * was about creating a new page); null if not known (that should not happen).
+ * - oldIsRedirect (bool|null): whether the page was a redirect before the change. Lazy-loaded,
+ * can be null; use wasRedirect() instead of direct access.
+ * - oldCountable (bool|null): whether the page was countable before the change (or null
+ * if we don't have that information)
+ *