xpath parsing of xs:* built-in list types

[digre]

From XPATH-Function 3.1:
18.3 Constructor functions for XML Schema built-in list types
Each of the three built-in list types defined in [XML Schema Part 2: Datatypes Second Edition], namely xs:NMTOKENS, xs:ENTITIES, and xs:IDREFS, has an associated constructor function.

The function signatures are as follows:

xs:NMTOKENS($arg as xs:anyAtomicType?) as xs:NMTOKEN*
xs:ENTITIES($arg as xs:anyAtomicType?) as xs:ENTITY*
xs:IDREFS($arg as xs:anyAtomicType?) as xs:IDREF*

These functions result in:
XPath: Function: 'xs:NMTOKENS' with 1 arguments not found

Also, the prompt within an xpath expression does not include these functions.