code: public function setTotalOrder( $totalOrder )
      {
          if (preg_match( '/^(?:\d*\.)?\d+$/', $totalOrder ) !== 1) {
              throw new InvalidArgumentException( sprintf( 'Order total value should be a non-negative number (%s)',
                  $totalOrder ) );
          }
  
          $this->totalOrder = (float)number_format( $totalOrder, 4, '.', '' );
  
          return $this;
      }
docs: @param  float $totalOrder
  
  @return $this