Functions, operators, and data types for XPath 3.1
serialize-json() function, which was defined in early working drafts of the specification, has been dropped.
Use serialize() with appropriate options in the second argument.
The array:put() function has been added.
The signature of fn:sort() and array:sort() has changed: the second argument is now a collation URI, and the comparison function becomes the third argument.
A new function map:find() is available.
The implementation of fn:transform() has been brought into line with the final W3C specification; there are significant changes.