[jitter] Jitter Recipe 36 Tiny Video

Hi,
I've spent some time with this patch, but I can't understand it yet.
In which Matrix and plane are the Coordinates to pick Frames in the texture.
I also don't understand what the jit.expr objekt in the gen_quads subpatch does. I guess it also somehow generates the coordinates but I don't see how to read them.

jit.expr @expr "(cell[0]%4.>0.)*(cell[0]%4.<3.)*0.2-0.1" "(cell[0]*0.5%2.>0.6)*0.15-0.075" "0." "(cell[0]%4.>0.)*(cell[0]%4.<3.)*0.1" "(cell[0]*0.5%2.>0.6)*0.1"

Can anyone help me there?
kind regards
ath