xpath (Nokogiri::XML::NodeSet)

    # File lib/nokogiri/xml/node_set.rb, line 113
          def xpath *paths
            ns = paths.last.is_a?(Hash) ? paths.pop :
              (document.root ? document.root.namespaces : {})

            sub_set = NodeSet.new(document)
            each do |node|
              sub_set += node.xpath(*(paths + [ns]))
            end
            document.decorate(sub_set)
            sub_set
          end