docs: public static byte[] getQualifier(final int level, final int order) {
      final byte[] suffix = (level + ":" + order).getBytes(CHARSET);
      final byte[] qualifier = new byte[RULE_PREFIX.length + suffix.length];
      System.arraycopy(RULE_PREFIX, 0, qualifier, 0, RULE_PREFIX.length);
      System.arraycopy(suffix, 0, qualifier, RULE_PREFIX.length, suffix.length);
      return qualifier;
    }