What is the name of "Fn" key for Awesome wm?

Question

For example:

awful.key({"Shift", }, "Left", volwidget.down)

How to find out what to write instead of "Shift" to use "Fn" key?

Answer 1

I've found the solution: the program xev.
If it runs, it doesn't show a Fn code. Actually it doesn't have to: X can't see that key.

Anyhow, it shows you the codes for "hot" keys, like Fn+LeftArrow (for volume down). In my case the name for that is XF86AudioLowerVolume and I can use it as such in configuration files.