Functions, operators, and data types for XPath 3.0
Namespaces defined in the XSLT, XPath, and XQuery specifications now generally begin
http://www.w3.org/2005/04/.... However, for the
xpath-datatypes namespace, the following
namespace URIs are recognized:
Saxon treats older versions of the namespace as synonyms for the current (2005/04) namespace
when matching type names appearing as an AtomicType in the SequenceType production and in the names of constructor functions.
If types in the xdt namespace are used during schema validation of source or result documents, however,
the current (2005/04) namespace must be used. Constructs that use these type names to refer to type annotations
on nodes, for example
attribute(*, xdt:anyAtomicType) must also use the current namespace.
The namespace for error codes is hardly used, but it is nominally
http://www.w3.org/2004/07/xqt-errors. Unlike the others, this namespace
has not been changed in successive working drafts.