Function xml_xpath_leading 

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

Implements the EXSLT - Sets leading() function: node-set set:leading (node-set, node-set) @nodes1 and @nodes2 are sorted by document order, then #exslSetsLeadingSorted is called.

Returns the nodes in @nodes1 that precede the first node in @nodes2 in document order, or an empty node-set if @nodes1 doesn’t contain @nodes2

Note

In original libxml, if nodes2 is NULL or empty, return nodes1.
However, this function returns the clone of nodes1.