URL("http://foo.co.jp/aaa/111.htm")
URL("/aaa/222.htm", "http://foo.co.jp/xxx/111.htm")
URL("../bbb/222.htm", "http://foo.co.jp/aaa/yyy/111.htm")
URL("ccc/222.htm", "http://foo.co.jp/aaa/bbb/111.htm")
URL("../../../bbb/222.htm", "http://foo.co.jp/aaa/xxx/111.htm")
URL("/bbb/222.htm")
URL("bbb/222.htm", "foo/111.htm")