docs: function(curve, location, length, distance) {
  		distance = distance == null ? 0 : distance;
  		var p = _pointAlongPath(curve, location, distance),
  			m = _gradientAtPoint(curve, p.location),
  			_theta2 = Math.atan(-1 / m),
  			y =  length / 2 * Math.sin(_theta2),
  			x =  length / 2 * Math.cos(_theta2);
  		return [{x:p.point.x + x, y:p.point.y + y}, {x:p.point.x - x, y:p.point.y - y}];
  	}