docs: function(curve, location) {
  		var p1 = _pointOnPath(curve, location),
  			p2 = _pointOnPath(curve.slice(0, curve.length - 1), location),
  			dy = p2.y - p1.y, dx = p2.x - p1.x;
  		return dy == 0 ? Infinity : Math.atan(dy / dx);
  	}