There are two conformance levels for XSLT 2.0, basic and schema-aware. Saxon-B implements the basic level. This allows only primitive data types plus xs:integer, it doesn't allow derived types such as xs:int.
There is however a switch in Saxon-B to recognize these types. Set
on the xsl:stylesheet element
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference