At the time of writing, work is in progress to implement assigning these types to variable values. While their datatype may be discoverable by the processor (again, via xquery:parse(), which conveniently returns an XML representation of the parsed tokens and their types), including support for these lends weight to the argument for adding optional attribute as to Schematron's let to express the datatype, which should also remove the need to support xsl:variable in an XSLT implementation.