enable show origin in preferences. that’ll show you 0,0,0. -Z is below the origin and +Z above. if you’re in metric mode, each line crossing is 5mm steps.
I think there is another small bug. My test piece is a cylinder and when I set the layer filter to { box: { x:[-4,4], y:[-4,4], z:[-100,100] } } it will not show any tool paths if there is no change in z along the part. In this case it was the x axis cut direction. If I change it to the y axis for cut direction it will produce a tool path. Hope this makes sense. I can dive deeper into the explanation if you need more info. I appreciate your work on this project. I think this small addition is so huge as it makes it possible to do intricate details without running the entire surface.
any segment of the path not fully inside the box will be omitted. meaning that long segments will not be clipped against the box. this may be the issue