Before, everything was simple: XSLT 1.0 used XPath 1.0.

Now it's slightly more complex:

• XSLT 2.0 uses XPath 2.0
• XPath 2.0 is a subset of XQuery 1.0
• The data model is now described in XQuery 1.0 and XPath 2.0 Data Model
• XPath functions are in XQuery 1.0 and XPath 2.0 Functions and Operators Version 1.0