private static boolean isReserved(char c) {
    switch (c) {
      case '<':
      case '>':
      case ':':
      case '"':
      case '|':
      case '?':
      case '*':
        return true;
      default:
        return c <= 31;
    }
  }
Checks if c is one of the reserved characters that aren't allowed in Windows file names.
jimfs/src/main/java/com/google/common/jimfs/WindowsPathType.java