. . _:vb16005 _:vb16004 . _:vb16005 . . _:vb16003 _:vb16005 . "This property points from a gr:Offering to additional offerings that can only be obtained in combination with the first offering. This can be used to model supplements and extensions that are available for a surcharge. Any gr:PriceSpecification attached to the secondary offering is to be understood as an additional charge."@en . _:vb16003 . "add-on (0..*)"@en . _:vb16004 . _:vb16003 . _:vb16004 .