- * event since the last invocation. The handler must either act upon the event immediately
- * or preserve it for later handling.
+ * event since the last invocation.
+ *
+ * In order to ensure no [`Event`]s are lost, implementors of this trait will persist [`Event`]s
+ * and replay any unhandled events on startup. An [`Event`] is considered handled when
+ * [`process_pending_events`] returns, thus handlers MUST fully handle [`Event`]s and persist any
+ * relevant changes to disk *before* returning.
+ *
+ * Further, because an application may crash between an [`Event`] being handled and the
+ * implementor of this trait being re-serialized, [`Event`] handling must be idempotent - in
+ * effect, [`Event`]s may be replayed.