@Override
      public String getLabel(int ordinal) {
        // Unused
        throw new UnsupportedOperationException(
          "getLabel should not be used in VisibilityExpressionResolver");
      }
This implementation creates tags by expanding expression using label ordinal. Labels will be
serialized in sorted order of it's ordinal.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/DefaultVisibilityExpressionResolver.java