code: function $version(byte) {
      version = (version << 8) | byte;
      if (++offset < 4) return $version;
      if (version >= 2 && version <= 3) {
        offset = 0;
        return $num;
      }
      throw new Error("Invalid version number " + num);
    }
docs: The version is stored as an unsigned 32 integer in network byte order. It must be version 2 or 3.