What do I use as the modifier when referencing the 'fn' key on a Mac?

I’m having trouble finding out what letter to use for a modifier for key/mouse binding, when using the ‘fn’ key as a modifier.

Can someone let me know or at least point me to some resource?

The ‘fn’ key may not actually register any keycode to the OS, instead be used just by the firmware.

You can use ‘xev’ to see if you notice any events when you push the key, but my guess is only fn+something else trigger any key events that get sent to the OS.

Thanks for the reply.

Checkig with xev, the key shows no events. But after some searching, I do get an event from the fn key using evtest:

Event: time 1642525632.563504, type 1 (EV_KEY), code 464 (KEY_FN), value 1
Event: time 1642525632.563504, -------------- SYN_REPORT ------------
Event: time 1642525632.691492, type 1 (EV_KEY), code 464 (KEY_FN), value 0
Event: time 1642525632.691492, -------------- SYN_REPORT ------------

I’ve seen KEY_XXX and the use of keycodes around in my searches, I think with xmodmap or something like that.

Might it still be possible even though there’s no output from the xev?

The fn key is a key used by your firmware. And yes fn + some other key will sometimes produce a keycode for the OS. It depends on the laptop what the fn key does, and nothing the os or fvwm can do about that.

In short you can’t make fn a modifier.

Ty for your help thus far, I do appreciate it.

I’m very curious though, of why the keyboard generates a key code that X11 doesn’t recognize. X11 recognizes other codes… but how? And why would this code be missed by X11 when clearly it sends a unique key code and the proper associated key (KEY_FN).

Would it even be feasible to comb through the X11 code and see if something can be added? I have done this before on a different package (editing, not adding a keycode). It just seems possible to me.

Anybody else’s thoughts?