This is used to enumerate over a record store and may travel in either direction. If the {@link RecordStore} has been closed then {@link RecordStoreNotOpenException} must be thrown even if it was later re-opened. When closed the previous and next methods will return {@code null}. If a {@link RecordStore} is modified during enumeration then some records may become invalid, for this a {@link RecordListener} may be used to be notified when records are added or removed. {@link RecordComparator} may be used to modify the iteration order and the {@link RecordFilter} may be used to remove undesired entries.