Editing Apple Aluminium Keyboard (section)

==Protocol==
Beside media key reports, the [[USB]] HID protocol format is the standard [[6KRO]] boot protocol except that it is only 5KRO to give room for a vendor-specific byte for the Fn key. Only Apple's own keyboard driver will recognise that byte while compliant HID drivers will ignore it.
A host that ignores the keyboard's "Report Descriptor" (such as many PC BIOS:es) will see the keyboard reporting the Fn key as a Rollover error code when pressed and as no key (zero) otherwise.

[[Bluetooth]] keyboards talk the same HID protocol as USB, just over Bluetooth's transport rather than over USB's transport layer.