The primitive type xs:NOTATION represents a reference to an XML notation. Notations are a way to indicate how to interpret non-XML content that is rarely used in the domain of XQuery and XML Schema. xs:NOTATION is an abstract type, and as such, you cannot construct values that have the type xs:NOTATION. It is possible to create user-defined types that are restrictions of xs:NOTATION, which do have type constructors associated with them. These type constructors have the constraint that they will only accept a literal string as an argument, not an evaluated expression.