Function xml_xpath_difference 

pub fn xml_xpath_difference(
    nodes1: Option<&XmlNodeSet>,
    nodes2: Option<&XmlNodeSet>,
) -> Option<Box<XmlNodeSet>>

Implements the EXSLT - Sets difference() function: node-set set:difference (node-set, node-set)

Returns the difference between the two node sets.

Note

In original libxml, if node2 is empty, return nodes1.
However, this function returns the clone of nodes1.