I know how to set up keybindings where you have to hold down one of the keys of type KeyMask. Which are: Alts, Ctrls, Windowskeys. Also, giving 0 as the KeyMask can be used to define single-key commands.
But I cannot assign arbitrary keys as KeyMask. Most keys are of type KeySym and with explicit conversions it does not work.
How can you assign arbitrary key combos? Or is that only possible with far too much hacking?
for example F1+F2