I made you a lil' drawing.
You might also want to take a look at :
https://github.com/elliotfontaine/vsmaptools/blob/v2.1.0/classes/map_piece.gd (for how I do it)
https://wiki.vintagestory.at/index.php/Modding:Deserializing_protobufs_from_the_command_line
https://github.com/bluelightning32/vs-proto/blob/80ff05afa98af324425ef6f3e5f12b4bea9e6a3f/schema-1.21.0.rc.3.proto#L72C1-L74C2