Rough outline to get you hacking: Run `setxkbmap -print | xkbcomp -xkb - -` and edit super/hyper/meta keys to your liking. Install result with `xkbcomp my-cool-layout.xkb $DISPLAY`.
IMO APL is best implemented as a new input method rather than a layout, add a new .mim file into /usr/share/m17n.
Rough outline to get you hacking: Run `setxkbmap -print | xkbcomp -xkb - -` and edit super/hyper/meta keys to your liking. Install result with `xkbcomp my-cool-layout.xkb $DISPLAY`.
IMO APL is best implemented as a new input method rather than a layout, add a new .mim file into /usr/share/m17n.