docs: function( bodyA, bodyB, stiffness, targetLength ){
  
              var cst;
  
              if (!bodyA || !bodyB){
  
                  return false;
              }
  
              cst = {
                  id: Physics.util.uniqueId('dis-constraint'),
                  type: 'dis',
                  bodyA: bodyA,
                  bodyB: bodyB,
                  stiffness: stiffness || 0.5,
                  targetLength: targetLength || bodyB.state.pos.dist( bodyA.state.pos )
              };
  
              cst.targetLengthSq = cst.targetLength * cst.targetLength;
  
              this._distanceConstraints.push( cst );
              return cst;
          }