hpricot：Hpricot::Traverse#css_path

>> require "hpricot"
=> true
>> doc = Hpricot('<p>foo1</p><p>foo2</p>')
=> #<Hpricot::Doc {elem <p> "foo1" </p>} {elem <p> "foo2" </p>}>
>> doc.css_path
=> nil
>> doc.search("p").css_path
NoMethodError: undefined method `css_path' for #<Hpricot::Elements:0xb7a2a230>
	from (irb):4
	from :0
>> doc.at("p").css_path
=> "p:nth(0)"
>> doc.search("p")[1].css_path
=> "p:nth(1)"
>> doc = Hpricot('<p id="foo">foo1</p><p>foo2</p>')
=> #<Hpricot::Doc {elem <p id="foo"> "foo1" </p>} {elem <p> "foo2" </p>}>
>> doc.at("p").css_path
=> "#foo"