I made this list a long time ago when I found a website that explained the various values. Hope it helps someone that finds this in the future.
These are the directly addressable modifier keys:
[mod:alt] alt key (meaning either alt key)
[mod:lalt] left alt key
[mod:ralt] right alt key
[mod:ctrl] control key (meaning either control key)
[mod:lctrl] left control key
[mod:rctrl] right control key
[mod:shift] shift key (meaning either shift key)
[mod:lshift] left shift key
[mod:rshift] right shift key
These can be combined by direct concatenation into key AND key like this:[mod:altctrl]
[mod:altlctrl]
[mod:altrctrl]
[mod:altshift]
[mod:altlshift]
[mod:altrshift]
[mod:laltctrl]
[mod:laltlctrl]
[mod:laltrctrl]
[mod:laltshift]
[mod:laltlshift]
[mod:laltrshift]
[mod:raltctrl]
[mod:raltlctrl]
[mod:raltrctrl]
[mod:raltshift]
[mod:raltlshift]
[mod:raltrshift]
[mod:ctrlshift]
[mod:ctrllshift]
[mod:ctrlrshift]
[mod:lctrlshift]
[mod:lctrllshift]
[mod:lctrlrshift]
[mod:rctrlshift]
[mod:rctrllshift]
[mod:rctrlrshift]
[mod:altctrlshift]
[mod:altctrllshift]
[mod:altctrlrshift]
[mod:altlctrlshift]
[mod:altlctrllshift]
[mod:altlctrlrshift]
[mod:altrctrlshift]