TF = isempty (S) is true for the shape solid.Shape () returns and for the result of a boolean that leaves no material, such as the intersection of shapes that do not meet. A boolean returns the empty shape rather than raising an error, so a script tests for it here. It has no volume, area, faces or extent, and solid.Shape.write refuses it. For an array of shapes, TF is true when the array has no elements.

 A = solid.box (10, 10, 10);
 isempty (intersect (A, translate (A, [20, 0, 0])))
 ⇒ 1
 isempty (intersect (A, translate (A, [5, 0, 0])))
 ⇒ 0

Source Code: solid.Shape