docs: function (data) {
      // Add property to hold internal values
      Object.defineProperty(this, '_', {
          enumerable: false,
          configurable: false,
          writable: false,
          value: {
              dt: this._clone(data),
              ev: {},
              df: {},
              sp: false,
              ct: 0
          }
      });
      // Assign keys
      for (var key in this._.dt) {
          this._addProperty(key);
      }
  }