The basic string type that is intended to represent generic character data is called, appropriately, xs:string. The xs:string type is not the default type for untyped values. If a value is selected from an input document with no schema, the value is given the type xs:untypedAtomic, not xs:string. However, it is easy enough to cast an untyped value to xs:string. In fact, you can cast a value of any type to xs:string and cast an xs:string value to any type.

The xs:string type is a primitive type from which a number of other types are derived. All of the operations and functions that can be performed on xs:string values can also be performed on values whose types are restrictions of xs:string. This includes user-defined types that appear in a schema, as well as built-in derived types such as xs:token, xs:language, and xs:ID. For a complete explanation of the built-in types, see Appendix B.