以 http://www.example.com/path/page.html 这个 URL 作为基准页面
http://subdomain.example.com/
等效 //subdomain.example.com
http://www.example.com/path/page2.html
等效 page2.html
http://www.example.com/index.html
等效 /index.html
http://www.example.com/path2/page.html
等效 ../path2/page.html
http://www.example.com/path/page.html#f=bar
等效 #f=bar
http://www.example.com/path/page.html?q=foo
等效 ?q=foo