@Override
      public int getLabelOrdinal(String label) {
        Integer ordinal = null;
        ordinal = labels.get(label);
        if (ordinal != null) {
          return ordinal.intValue();
        }
        return VisibilityConstants.NON_EXIST_LABEL_ORDINAL;
      }
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