code: function(obj) {
                  if (obj.normal || (obj.start && obj.end)) { return obj.isParallelTo(this); }
                  var theta = this.direction.angleFrom(obj.direction);
                  return (Math.abs(theta) <= sylvester.precision || Math.abs(theta - Math.PI) <= sylvester.precision);
                }
docs: Returns true if the line is parallel to the argument. Here, 'parallel to' means that the argument's direction is either parallel or antiparallel to the line's own direction. A line is parallel to a plane if the two do not have a unique intersection.