code: function(orthonormalbasis, depth) {
              // first extrude in the regular Z plane:
              if (!(orthonormalbasis instanceof CSG.OrthoNormalBasis)) {
                  throw new Error("extrudeInPlane: the first parameter should be a CSG.OrthoNormalBasis");
              }
              var extruded = this.extrude({
                  offset: [0, 0, depth]
              });
              var matrix = orthonormalbasis.getInverseProjectionMatrix();
              extruded = extruded.transform(matrix);
              return extruded;
          }
docs: extrude the CAG in a certain plane. Giving just a plane is not enough, multiple different extrusions in the same plane would be possible by rotating around the plane's origin. An additional right-hand vector should be specified as well, and this is exactly a CSG.OrthoNormalBasis. orthonormalbasis: characterizes the plane in which to extrude depth: thickness of the extruded shape. Extrusion is done symmetrically above and below the plane.