# File lib/xml/dom2/xpath.rb, line 274
      def __collectDescendatNS(ns = {})
        childNodes.each do |node|
          next if node.nodeType != ELEMENT_NODE
          prefix = node.prefix
          uri = node.namespaceURI
          ns[prefix] = uri unless ns.has_key?(prefix)
          node.__collectDescendatNS(ns)
        end
      end