code: function setAnimationFrame(idx) {
           this.current.idx = (idx || 0) % this.current.length;
           return this.setRegion(this.getAnimationFrameObjectByIndex(this.current.idx));
         }
docs: force the current animation frame index.
  @name setAnimationFrame
  @memberOf me.Sprite.prototype
  @function
  @param {Number} [index=0] animation frame index
  @return {me.Sprite} Reference to this object for method chaining
  @example
  // reset the current animation to the first frame
  this.setAnimationFrame();