docs: function cropVertically( img ) {
    var zoom = this.width / img.width;
    var y = 0;
    if( this.cropping == 'body' ) {
      y = 0.5 * (this.height - img.height * zoom);
    }
    else if( this.cropping == 'tail' ) {
      y = this.height - img.height * zoom;
    }
    draw.call( this, img, 0, y, zoom );
  }