public BucketId getSuperbucket() {
            return superbucket;
        }
<p>Enables transparent iteration of super/sub-buckets</p>

<p>Thread safety: safe for threads to hold their own iterators (no shared state),
as long as they also hold the ProgressToken object associated with it. No two
VisitorIterator instances may share the same progress token instance at the
same time.
Concurrent access to a single VisitorIterator instance is not safe and must
be handled atomically by the caller.</p>

@author vekterli
documentapi/src/main/java/com/yahoo/documentapi/VisitorIterator.java