Multiple constraints vs user constraint

[Andy Croft]

My scenario involves a series of bodies linked together in a chain-like fashion.  The goal is to create a "greenstick" object that is pliable but not rope-like in regards to how the joints behave.  An example might be a diving board or a bent paperclip. 

I'm working in AS3.  I'll try to be concise, my questions are in bold orange.  Any guidance would be greatly appreciated :)

I'm trying to devise an efficient method of combining the following constraint effects:

• PivotJoint: stiff, end-to-end join between two bodies
• AngleJoint: narrow angle of min/max to limit the chain looping back onto itself (hopefully)
• WeldJoint: elastic, high frequency… hope to create an "angular tension" between two bodies

Initially I made a class containing those three constraint types.  The class provided an interface to easily link the two bodies.  It works but it seems inefficient to have a class containing three separate constraints that the simulation will iterate over to accomplish ONE goal. 

A UserConstraint seems the logical choice, it could handle all the calculations in a single object.  Unfortunately, I am having a hard time understanding how the interface works in overriding the predefined function calls.

Looking at the documentation (Constraints.pdf), I attempted to combine the example Pivot and Angle joints and was confounded. 

• Override Functions: I understand the "override functions" pass an array/vector of numbers to be initialized/manipulated.  These values are used internally somehow in the sausage-factory of physics. 
  
• How are the dimensions and content of these arrays determined?  For instance, comparing the PivotJoint to the AngleJoint:
  

  PivotJoint: Page 13 in Constraints.pdf
  

  override public function __position(err:Vector.<Number>):void
  {
      err[0] = (body2.position.x + _rel2.x) - (body1.position.x + _rel1.x);
      err[1] = (body2.position.y + _rel2.y) - (body1.position.y + _rel1.y);
  }//END FUNCTION: __position

  
  AngleJoint: Page 14 in Constraints.pdf

  override public function __position(err:Vector.<Number>):void
  {
      err[0] = error; //determined in __prepare() function already
  }//END FUNCTION: __position

• HAXE vs AS3: Looking at the AngleJoint example in the documentation, I see a Vec3 accessing a property named w.  I assume this is the "scalar weight" mentioned under the definition of the AngleJoint (page 6).
  

  public override function __velocity(err:TArray<Float>):Void {
      var v1 = body1.constraintVelocity;
      var v2 = body2.constraintVelocity;
      err[0] = (weight * (ratio * v2.w)) - v1.w;
  }

• Is there an equivalent property in AS3?
• If not, will this confound my effort to emulate the AngleJoint?