How to make ISO_Level5_Shift work?

I wanted to add more levels to my keyboard layouts, so I decided to enable level5 key. I’ve already had level3 on Menu, and would like to map RAlt to ISO_Level5_Shift. However, setxkbmap has no option for that. /usr/share/X11/xkb/rules/evdev.lst contains only the following options in regard to lv5 switch: lv5:lsgt_switch_lock lv5:ralt_switch_lock lv5:lwin_switch_lock lv5:rwin_switch_lock As if mapping a simple key is not possible. This already hinted on troubles. Knowing what setxkbmap does internally, it’s easy to construct an option to enable lv5 switch and set to right Alt: -option "lv5:ralt_switch" And, despite that setxkbmap takes this option and returns with success, there’s no mapping. ***** After finding an answer to a similar question [here](https://askubuntu.com/a/973273) I’ve constructed a custom xkbcomp file. xkb_keymap { xkb_geometry { include "pc(pc104)" }; xkb_keycodes { include "evdev" include "aliases(qwerty)" }; xkb_types { include "complete" }; xkb_compatibility { include "complete" include "ledscroll(group_lock)" }; xkb_symbols { include "pc+us+ru:2+inet(evdev)" include "group(rctrl_rshift_toggle)" include "ctrl(swapcaps)" include "keypad(oss)" include "kpdl(dot)" include "terminate(ctrl_alt_bksp)" include "level3(modifier_mapping)" include "level3(menu_switch)" include "level5(modifier_mapping)" include "level5(ralt_switch)" key { type= "EIGHT_LEVEL", symbols[Group1]= [ n, N, n, n, u, i, o, p ], symbols[Group2]= [ Cyrillic_te, Cyrillic_TE, n, n, u, i, o, p ] }; }; }; This should assign Menu key to be ISO_Level3_Shift and RAlt to be ISO_Level5_Shift. And the keys are assigned, but there is an error: $ xkbcomp ~/new.xkbcomp.xkb :0 Error: Key added to map for multiple modifiers Using Mod3, ignoring Mod5. xkbcomp returns with code 0, despite that there was an error. The mapping on key N should have made levels 5 to 8 “u”, “i”, “o” and “p”, but instead RAlt sends the usual n and N on all eight levels (if levels >4 actually work). In attempt to determine, how to solve this error, I’ve found, that `` is set in… the very rules file for “pc”. /usr/share/X11/xkb/symbols/pc: xkb_symbols "pc105" { … // Fake keys for virtualreal modifiers mapping: key { [ ISO_Level3_Shift ] }; key { [ Mode_switch ] }; modifier_map Mod5 { , }; … }; And here is another weird thing: I include pc104 keyboard model, but this code refers to pc105 and shouldn’t be sourced at all. However… xkb_symbols "pc104" is nowhere to be found. And this “symbols/pc” file is the only other file in /usr/share/X11/xkb/ that sets or modifies ` assignment to Mod* keys. The other file being “symbols/level5” file, which does it in xkb_symbols "modifier_mapping"`. // Ensure a mapping to a real modifier for LevelFive. partial modifier_keys xkb_symbols "modifier_mapping" { replace key { type[Group1] = "ONE_LEVEL", symbols[Group1] = [ ISO_Level5_Shift ] }; modifier_map Mod3 { }; }; I think, that this conflict may prevent both lv3 switch and lv5 switch to work at the same time, but I’m not sure. It’s concerning, that in [another answer](https://askubuntu.com/a/41585) , Mode_switch key is present among Mod* keys, and after loading my new.xkbcomp.xkb I don’t see it anywhere: $ xmodmap -pm xmodmap: up to 4 keys per modifier, (keycodes in parentheses): shift Shift_L (0x32), Shift_R (0x3e) lock Caps_Lock (0x25) control Control_L (0x42), Control_R (0x69) mod1 Alt_L (0x40), Meta_L (0xcd) mod2 Num_Lock (0x4d) mod3 ISO_Level5_Shift (0xcb) mod4 Super_L (0x85), Super_R (0x86), Super_L (0xce), Hyper_L (0xcf) mod5 ISO_Level3_Shift (0x5c)