引用别人的文档:
http://wenku.baidu.com/link?url=3wGAJZZRnIJAe3gp65Q0L0BKzCEKPlmyCsOd_jrwjp_wixEENOXPGR1RgVVDv4dVwq7NzYgoBnTbuK37ki5p-JdsU2lk5Zq8YJv70FRVp5e&qq-pf-to=pcqq.discussion