XForms 2.0: XPath expression module

This module defines how XPath could be used for addressing instance data nodes in binding expressions, to express constraints, and to specify calculations in XForms. This module is based on XPath 2.0, but an XPath 1.0 backwards compatibility mode is provided to ensure that nearly all XPath 1.0 expressions continue to deliver the same result with XPath 2.0. This module also defines the XForms Function Library which contains additional functions that are useful for creating forms.