class Nokogiri::CSS::XPathVisitor

def visit_pseudo_class(node)
  if node.value.first.is_a?(Nokogiri::CSS::Node) && (node.value.first.type == :FUNCTION)
    node.value.first.accept(self)
  else
    msg = :"visit_pseudo_class_#{node.value.first.gsub(/[(]/, "")}"
    return send(msg, node) if respond_to?(msg)
    case node.value.first
    when "first" then "position()=1"
    when "first-child" then "count(preceding-sibling::*)=0"
    when "last" then "position()=last()"
    when "last-child" then "count(following-sibling::*)=0"
    when "first-of-type" then "position()=1"
    when "last-of-type" then "position()=last()"
    when "only-child" then "count(preceding-sibling::*)=0 and count(following-sibling::*)=0"
    when "only-of-type" then "last()=1"
    when "empty" then "not(node())"
    when "parent" then "node()"
    when "root" then "not(parent::*)"
    else
      "nokogiri:#{node.value.first}(.)"
    end
  end
end