Note that the first expected argument to xcopies() is the spacing argument, so you do not need to supply the spacing= argument name. Similarly, ycopies() makes a line of evenly spaced copies centered ...

The acronym VNF stands for Vertices 'N' Faces. You have probably already come across the concept of vertices and faces when working with the OpenSCAD built-in module polyhedron(). A polyhedron() in it ...