public interface BusEvent<T>
+-----------+
| CLEAN | +------------ MAGIC_CLEAN
+-----------+
+-----------+
| DIRTY | +------------ SMUDGE
+-----------+
no state change +------------ CLEAN_ORDER_ERROR
+----------------------+
| CLEANING_ORDERED | +--- CLEAN_ORDER_OK
+----------------------+
+-------------------+
| BEING_CLEANED | +------ CLEAN_STARTED
+-------------------+
+-------------+
| CLEANED | +------------ CLEAN_OK
+-------------+
+-----------+
| FAIL | +-------------- CLEAN_ERROR
+-----------+
+--------------+
| ABORTED | +----------- CLEAN_ABORTED
+--------------+
+--------+
| * | +----------------- STATE_CHANGE_HACK
+--------+