[CrossVR]

At first I wasn't sure why it contained a separate Unix line feed when you would already be able to detect a Unix to DOS conversion from the DOS line ending:

0D 0A 1A 0A -> 0D 0D 0A 1A 0D 0A

But of course this isn't to try and detect a Unix-to-DOS conversion, it's to detect a roundtrip DOS-to-Unix-to-DOS conversion:

0D 0A 1A 0A -> 0A 1A 0A -> 0D 0A 1A 0D 0A

Certainly a very well thought-out magic number.

[layer8]

Unix2dos is idempotent on CRLF, it doesn’t change it to CRCRLF. Therefore converted singular LFs elsewhere in the file wouldn’t be recognized by the magic-number check if it only contained CRLF. This isn’t about roundtrip conversion.

[Dwedit]

It's also detecting when a file on DOS/Windows is opened in "ASCII mode" rather than binary mode. When opened in ASCII mode, "\r\n" is automatically converted to "\n" upon reading the data.