docs: def format_system_message(errno):
      """
      Call FormatMessage with a system error number to retrieve
      the descriptive error message.
      """
      # first some flags used by FormatMessageW
      ALLOCATE_BUFFER = 0x100
      ARGUMENT_ARRAY = 0x2000
      FROM_HMODULE = 0x800
      FROM_STRING = 0x400
      FROM_SYSTEM = 0x1000
      IGNORE_INSERTS = 0x200
  
      # Let FormatMessageW allocate the buffer (we'll free it below)
      # Also, let it know we want a system error message.
      flags = ALLOCATE_BUFFER | FROM_SYSTEM
      source = None
      message_id = errno
      language_id = 0
      result_buffer = ctypes.wintypes.LPWSTR()
      buffer_size = 0
      arguments = None
      format_bytes = ctypes.windll.kernel32.FormatMessageW(
          flags,
          source,
          message_id,
          language_id,
          ctypes.byref(result_buffer),
          buffer_size,
          arguments,
      )
      # note the following will cause an infinite loop if GetLastError
      #  repeatedly returns an error that cannot be formatted, although
      #  this should not happen.
      handle_nonzero_success(format_bytes)
      message = result_buffer.value
      ctypes.windll.kernel32.LocalFree(result_buffer)
      return message