def first( path_stack, node )
      #puts "#{depth}) Entering match( #{path.inspect}, #{tree.inspect} )"
      return nil if path.size == 0

      case path[0]
      when :document
        # do nothing 
        return first( path[1..-1], node )
      when :child
        #for c in node.children
        node.children.each do |c|
          #puts "#{depth}) CHILD checking #{name(c)}"
          r = first( path[1..-1], c )
          #puts "#{depth}) RETURNING #{r.inspect}" if r
          return r if r
        end
      when :qname
        name = path[2]
        #puts "#{depth}) QNAME #{name(tree)} == #{name} (path => #{path.size})"
        if node.name == name
          #puts "#{depth}) RETURNING #{tree.inspect}" if path.size == 3
          return node if path.size == 3
          return first( path[3..-1], node )
        else
          return nil
        end
      when :descendant_or_self
        r = first( path[1..-1], node )
        return r if r
        #for c in node.children
        node.children.each do |c|
          r = first( path, c )
          return r if r
        end
      when :node
        return first( path[1..-1], node )
      when :any
        return first( path[1..-1], node )
      end
      return nil
    end
def first( path_stack, node )
      #puts "#{depth}) Entering match( #{path.inspect}, #{tree.inspect} )"
      return nil if path.size == 0

      case path[0]
      when :document
        # do nothing 
        return first( path[1..-1], node )
      when :child
        #for c in node.children
        node.children.each do |c|
          #puts "#{depth}) CHILD checking #{name(c)}"
          r = first( path[1..-1], c )
          #puts "#{depth}) RETURNING #{r.inspect}" if r
          return r if r
        end
      when :qname
        name = path[2]
        #puts "#{depth}) QNAME #{name(tree)} == #{name} (path => #{path.size})"
        if node.name == name
          #puts "#{depth}) RETURNING #{tree.inspect}" if path.size == 3
          return node if path.size == 3
          return first( path[3..-1], node )
        else
          return nil
        end
      when :descendant_or_self
        r = first( path[1..-1], node )
        return r if r
        #for c in node.children
        node.children.each do |c|
          r = first( path, c )
          return r if r
        end
      when :node
        return first( path[1..-1], node )
      when :any
        return first( path[1..-1], node )
      end
      return nil
    end
Performs a depth-first (document order) XPath search, and returns the
 first match.  This is the fastest, lightest way to return a single result.

 FIXME: This method is incomplete!