docs: public static boolean isSinglePositionPrefix(FieldInfo fieldInfo,
        String prefix) throws IOException {
      if (fieldInfo == null) {
        throw new IOException("no fieldInfo");
      } else {
        String info = fieldInfo.getAttribute(
            MtasCodecPostingsFormat.MTAS_FIELDINFO_ATTRIBUTE_PREFIX_SINGLE_POSITION);
        if (info == null) {
          throw new IOException("no "
              + MtasCodecPostingsFormat.MTAS_FIELDINFO_ATTRIBUTE_PREFIX_SINGLE_POSITION);
        } else {
          return Arrays.asList(info.split(Pattern.quote(MtasToken.DELIMITER)))
              .contains(prefix);
        }
      }
    }