no, those are just HTML Elements and the gojs diagram is being drawn on top of the HTML Table layout. So only completely white rectangles with border are gojs nodes.
Earlier I had not included making sure the fromSpot and toSpot were limited to particular sides, depending on “openness”, but now I have done that too, and I still do not see any problem.
So I do not see how what I have tried is different from what you have.