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