XML Path Language (XPath) 2.0

XPath 2.0 is an expression language that allows
the processing of values conforming to the data model defined in
[XQuery/XPath Data Model (XDM)]. The data
model provides a tree representation of XML documents as well as
atomic values such as integers, strings, and booleans, and
sequences that may contain both references to nodes in an XML
document and atomic values. The result of an XPath expression may
be a selection of nodes from the input documents, or an atomic
value, or more generally, any sequence allowed by the data model.
The name of the language derives from its most distinctive feature,
the path expression, which provides a means of hierarchic
addressing of the nodes in an XML tree. XPath 2.0 is a superset of
[XPath 1.0], with the added capability to
support a richer set of data types, and to take advantage of the
type information that becomes available when documents are
validated using XML Schema. A backwards compatibility mode is
provided to ensure that nearly all XPath 1.0 expressions continue
to deliver the same result with XPath 2.0; exceptions to this
policy are noted in [I
Backwards Compatibility with XPath 1.0].