docs: function (formatSymbols) {
              if (!formatSymbols) {
                  formatSymbols = {
                      decimalSeparator : this._decimal,
                      groupingSeparator : this._grouping,
                      strictGrouping : this._strictGrouping
                  };
              } else {
                  formatSymbols.decimalSeparator = formatSymbols.decimalSeparator || this._decimal;
                  formatSymbols.groupingSeparator = formatSymbols.groupingSeparator || this._grouping;
                  formatSymbols.strictGrouping = formatSymbols.strictGrouping != null
                          ? formatSymbols.strictGrouping
                          : this._strictGrouping;
              }
  
              return formatSymbols;
          }