code: function(t) {
  
              if (!this.isDifferentiable()) return null;
  
              if (t < 0) t = 0;
              else if (t > 1) t = 1;
  
              var skeletonPoints = this.getSkeletonPoints(t);
  
              var p1 = skeletonPoints.startControlPoint2;
              var p2 = skeletonPoints.dividerControlPoint1;
  
              var tangentStart = skeletonPoints.divider;
  
              var tangentLine = new Line(p1, p2);
              tangentLine.translate(tangentStart.x - p1.x, tangentStart.y - p1.y); // move so that tangent line starts at the point requested
  
              return tangentLine;
          }
docs: Returns a tangent line at requested `t`.