grep "compose:" /usr/share/X11/xkb/rules/base.lst
compose:ralt Right Alt
compose:lwin Left Win
compose:lwin-altgr 3rd level of Left Win
compose:rwin Right Win
compose:rwin-altgr 3rd level of Right Win
compose:menu Menu
compose:menu-altgr 3rd level of Menu
compose:lctrl Left Ctrl
compose:lctrl-altgr 3rd level of Left Ctrl
compose:rctrl Right Ctrl
compose:rctrl-altgr 3rd level of Right Ctrl
compose:caps Caps Lock
compose:caps-altgr 3rd level of Caps Lock
compose:102 <Less/Greater>
compose:102-altgr 3rd level of <Less/Greater>
compose:paus Pause
compose:prsc PrtSc
compose:sclk Scroll Lock