set:leading() returns the nodes in one node-set that come before the first node in the other node-set.
set:leading(nodeSet1, nodeSet2)nodeSet1The node set to find nodes in that precede the first node in the second node set.
nodeSet2The node set to compare against.
A node-set containing the nodes from nodeSet1 whose values precede the first node in nodeSet2.
Note: If the first node in nodeSet2 isn't contained in nodeSet1, an empty set is returned. If nodeSet2 is empty, then the result is nodeSet1.