code: function() {
              var data = {
                  duration: new Date() - this.getStartTime(),
                  currentFrame: this.currentFrame
              };
              
              data.toString = function() {
                  return (
                      'duration: ' + data.duration +
                      ', currentFrame: ' + data.currentFrame
                  );
              };
              
              this.onTween.fire(data);
              
              var runtimeAttributes = this.runtimeAttributes;
              
              for (var attr in runtimeAttributes) {
                  this.setAttribute(attr, this.doMethod(attr, runtimeAttributes[attr].start, runtimeAttributes[attr].end), runtimeAttributes[attr].unit); 
              }
              
              actualFrames += 1;
          }
docs: Feeds the starting and ending values for each animated attribute to doMethod once per frame, then applies the resulting value to the attribute(s).
  @private