code: function () {
        this.clearContext(this.contextTop || this.contextContainer);
  
        if (this.overlayImage) {
          this.contextContainer.drawImage(this.overlayImage, 0, 0);
        }
  
        // we render the top context - last object
        if (this.selection && this._groupSelector) {
          this._drawSelection();
        }
  
        // delegate rendering to group selection if one exists
        // used for drawing selection borders/corners
        var activeGroup = this.getActiveGroup();
        if (activeGroup) {
          activeGroup.render(this.contextTop);
        }
  
        this.fire('after:render');
  
        return this;
      }
docs: Method to render only the top canvas.
  Also used to render the group selection box.
  @method renderTop
  @return {fabric.Canvas} thisArg
  @chainable