The documentation for the com.sun.star.style.PageProperties (https://api.libreoffice.org/docs/idl/ref/servicecom_1_1sun_1_1star_1_1style_1_1PageProperties.html#a6fa54c86891f86d4750edc9ff3aacd93) service UserDefinedAttributes attribute says: "This com::sun::star::container::XNameContainer supports the service com::sun::star::xml::AttributeContainer." This is a useful note that can be included in documentation for other services that have the UserDefinedAttributes attribute: com.sun.star.table.CellProperties com.sun.star.drawing.GenericDrawPage com.sun.star.frame.XFrame2