> What happens when group of curves will be inside of solid or intersect the one?

Hi Petr, I may need an image of this to be certain that I understand your question.

But if I understand correctly, it doesn't matter where the curves are located, they can be anywhere along their plane normal and have the same effect.

This is because the solid doesn't interact with the curves directly - instead imagine that the curves are
moved along their plane normal to be placed just a little bit outside the bounding box of the solid (or surface), then extruded so that they push through to a little bit more than the other side of the bounding box of the solid.

This produces the same extrusion part no matter where the curves are placed along that normal direction.

Then the solid actually interacts with that extrusion.


I've now finished Union now to work properly with surfaces.

- Michael