Filters out all nodes in the node set, which do have descendant nodes in the same node set. This is useful if you do a combined query like //(a|b)[. &= $terms] and some 'b' nodes are nested within 'a' nodes, but you only want to see the innermost matches, i.e. the 'b' nodes, not the 'a' nodes containing 'b' nodes.
$node-set
The node set
Returns a node set containing nodes that do not have descendent nodes.
