code: function(begin, finish, duration, options) {
          this.playing = true;
          this.begin = begin;
          this.finish = finish;
          this.duration = duration;
          this.callbacks = options.callbacks;
          this.minFrameRate = options.minFrameRate || 30;
          this.time = 0;
          this.startTime = new Date().getTime();
          OpenLayers.Animation.stop(this.animationId);
          this.animationId = null;
          if (this.callbacks && this.callbacks.start) {
              this.callbacks.start.call(this, this.begin);
          }
          this.animationId = OpenLayers.Animation.start(
              OpenLayers.Function.bind(this.play, this)
          );
      }
docs: APIMethod: start
  Plays the Tween, and calls the callback method on each step
  
  Parameters:
  begin - {Object} values to start the animation with
  finish - {Object} values to finish the animation with
  duration - {int} duration of the tween (number of steps)
  options - {Object} hash of options (callbacks (start, eachStep, done),
  minFrameRate)