Can anyone clarify how the castling codes work

Castling string for 10x8 Gothic Chess. It seems very confusing to the uninitiated.

confusing

Kk = King landing spot when short castling

Kq = King landing spot when long castling

kRk = kingside Rook landing spot when short castling

qRq = queenside Rook landing spot when long castling

Thanks

I still don't get Kk = k4 while Kq = e4 etc

If you think about it, it's quite simple:

The 2 Ks in kk signify the King moving and which direction it's castling, also known as Kingside
The Q in kq mean Queenside castling
The R in kRk and qRq means the Rook movement

I think you're missing the crux of the matter. The k4 and e4 are based on the 14x14 coordinates grid. For example in XXL chess:

Kk':'m1','Kq':'c1','kRk':'l1','qRq':'d1

Therefore. The k4 and e4 are out of line so they have to be adjusted based on the grid.

It's not difficult but it's all based on 14x14 coordinates grid.

PGN4/FEN4 use the 14x14 grid, not the shown coordinates