code: public function setQuantityItems( $quantityItems )
      {
          if (preg_match( '/^\d+$/', $quantityItems ) !== 1) {
              throw new InvalidArgumentException( sprintf( 'Items quantity should be a non-negative integer (%s)',
                  $quantityItems ) );
          }
  
          $this->quantityItems = intval( $quantityItems );
  
          return $this;
      }
docs: @param  int $quantityItems
  
  @return $this