Support for the XPath not() function.
Support for the XPath true()/false() functions.
Default attribute namespaces.

When an attribute is prefixed with "xml" the default namespace should be used
automatically. This namespace is not registered on element level by default as
this namespace isn't registered manually, instead it's a "magic" namespace. This
also ensures we match the behaviour of libxml more closely, hopefully reducing
confusion.
Handle boolean values in predicate results.
Support for the XPath lang() function.