11.2. String XSLT Functions
The XSLT string function group includes four functions: system-property(), generate-id(), format-number(), and unparsed-entity-uri().
The system-property() function is not a string function in the purest sense, as it does not necessarily return a string as its function return type, but rather takes a string as a required argument. This function performs a sort of internal diagnostic check for system properties, and its resulting object is controlled by the namespace defining the system property.
The second function, generate-id(), enables the creation of unique identifiers for nodes in the input XML document instance. It can be used, for instance, to create an ID attribute for later use with the id() function.