now I'm having trouble with the grid setting. I tried:

grid 0.46um 0.34um 0.23um 0.17um
snap internal

but when I click randomly, the box accepts the unconstrained mouse position regardless. similarly cells can be moved unconstrained. I can see the grid being rendered though. any ideas?

snap internal

is what makes the position unconstrained. The command option that you want is

snap grid

(

snap on

is equivalent to

snap grid

and

snap off

is equivalent to

snap internal

).