docs: function(x, y) {
          if (this._translateX === undefined) { this._translateX = 0; }
          if (this._translateY === undefined) { this._translateY = 0; }
  
          if (x !== null && x !== undefined) { this._translateX = unit(x, 'px'); }
          if (y !== null && y !== undefined) { this._translateY = unit(y, 'px'); }
  
          this.translate = this._translateX + "," + this._translateY;
        }