code: function(obj) {
                  var theta;
                  if (obj.normal) {
                    // obj is a plane
                    theta = this.normal.angleFrom(obj.normal);
                    return (Math.abs(theta) <= sylvester.precision || Math.abs(Math.PI - theta) <= sylvester.precision);
                  } else if (obj.direction) {
                    // obj is a line
                    return this.normal.isPerpendicularTo(obj.direction);
                  }
                  return null;
                }
docs: Returns true iff the plane is parallel to the argument. Will return true if the planes are equal, or if you give a line and it lies in the plane.