How to emulate integrated numeric keypad cursor keys in linux - linux

Question

On many older laptops and some compact keyboards there is an integrated numeric keypad in the main keyboard area. This alternate keypad is activated with a special 'Fn' key next to the left Ctrl key.
As a programmer I learned to use the cursor movement keys (arrows, PgUp, PgDn etc.) and found it greatly improved my programming speed. And the benefits were not bound to just a single application as is the case with specialised shortcut keys.
On conventional PC keyboards, the 'Windows Key' can be used to emulate the 'Fn' key and a corresponding integrated numeric keypad. When I used to use MS Windows I found Autohotkey was able to map the keys using a simple script.
Recently I learned about xkb and how it can be used to map keystrokes at a very low level.
What is the xkb keyboard mapping profile that will emulate an integrated numeric keypad using the windows key as the fn key?
Hint(?): I suspect the file will look a lot like the '/usr/share/X11/xkb/symbols/keypad' file on a Debian-derivative linux distro. This 'keypad' file is included at the top of the '/usr/share/X11/xkb/symbols/pc' file.
The corresponding autohotkey script for reference (# == WinKey):
#8::Up
#k::Down
#u::Left
#o::Right
#7::Home
#j::End
#9::PgUp
#l::PgDn
#m::Insert
#.::Delete
;(Scroll with the left-over keys)
#i::WheelUp
#,::WheelDown
Note that all these keys need to work with any combination of Ctrl, Alt, Shift as well as the Windows Key.

Answer 1

Steps to install numeric keypad-like cursor keys on the main keyboard in Linux / XKB...
xkbcomp $DISPLAY original.xkb (just in case ;)
xkbcomp $DISPLAY custom.xkb
Edit custom.xkb
Add the following at the end of section: xkb_types "..." {
type "WinKeyAsFnKey" {
modifiers = Shift+Super;
map[Shift] = level2;
map[Super] = level3;
map[Super+Shift] = level3;
level_name[Level1] = "Base";
level_name[Level2] = "Caps";
level_name[Level3] = "Fn";
};
Add the following at the end of section xkb_symbols "..." {
key <AE07> {type="WinKeyAsFnKey",symbols[Group1]=[7,ampersand,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<HOME>,clearmods=Super)]};
key <AE08> {type="WinKeyAsFnKey",symbols[Group1]=[8,asterisk,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<UP>,clearmods=Super)]};
key <AE09> {type="WinKeyAsFnKey",symbols[Group1]=[9,parenleft,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<PGUP>,clearmods=Super)]};
key <AD07> {type="WinKeyAsFnKey",symbols[Group1]=[u,U,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<LEFT>,clearmods=Super)]};
key <AD09> {type="WinKeyAsFnKey",symbols[Group1]=[o,O,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<RGHT>,clearmods=Super)]};
key <AC07> {type="WinKeyAsFnKey",symbols[Group1]=[j,J,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<END>,clearmods=Super)]};
key <AC08> {type="WinKeyAsFnKey",symbols[Group1]=[k,K,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<DOWN>,clearmods=Super)]};
key <AC09> {type="WinKeyAsFnKey",symbols[Group1]=[l,L,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<PGDN>,clearmods=Super)]};
key <AB07> {type="WinKeyAsFnKey",symbols[Group1]=[m,M,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<INS>,clearmods=Super)]};
key <AB09> {type="WinKeyAsFnKey",symbols[Group1]=[period,greater,NoSymbol],actions=[NoAction(),NoAction(),RedirectKey(key=<DELE>,clearmods=Super)]};
Save custom.xkb
xkbcomp custom.xkb $DISPLAY
I'm still working on the mouse scroll with 'i' and ','.
EDIT:
The above solution does not play nice with Google Chrome and Chrome-based apps (like Slack).
Alternative approach is to use a programmable keyboard. I use an after-market PCB for a CoolerMaster Masterkeys S keyboard. The Easy AVR layout is available online (although currently the left win-key now doesn't work by itself...I use the right one).