Function not_a_device 

fn not_a_device(name: String) -> String

A name Windows keeps for a device (“CON”, “NUL”, “AUX”, “PRN”, “COM1”, “LPT1”…, whatever follows its first dot) taken out of its way with a “” before that dot: “Nul.md” would write to no file there, “aux.txt.md” too (“aux.txt.md” does not), and notes travel between systems.