what is the recommended way to remove rectangles from a mesh? I have tried table.remove from mesh.vertices, but it does not work.
Probably best to create a new mesh and copy across all but the rectangle you want, I should imagine it’s fairly quick - the problem with the table.remove is that it’ll probably leave a “hole” in the table which might confuse things.
Ok. I am currently using that technique in my program, so I will continue doing that. Thanks for the feedback. 
Quicker would be to collapse its vertices to a point. To be extra sure you could ensure that that point was very definitely “off screen”.
I’ve been using Andew’s method, it works fine.