Some suggestions about Relative coordinates and Absolute coordinates:
The upper X,Y represent Absolute coordinates.
The lower x,y represent Relative coordinates.
And have a switch represent which coordinates if there is not X or x or @
x100=x100,y0
y100=x0,y100
,100=x0,100
x100,100=x100,y100
X100,100=X100,Y100
d100<100=@100<100
In additon, any invalidating character represent comma "," e.g 100+100=100,100 ,and we can use the number keyboard handily.
Of course @ can be keeped. I don't dislike it.
Usually I use Relative coordinate only.So I hope @ can be omited.