As it says in TFA: > So to this day whenever a client connects, the first byte it sends is a literal "l" or "B" to inform the server of the client's byte orde

As it says in TFA: > So to this day whenever a client connects, the first byte it sends is a literal "l" or "B" to inform the server of the client's byte order. Where the byte order doesn't match the X server's byte order, the client is a "swapped client" in X server terminology So it's wherever the client doesn't match the server, which ever way around that is.