课程视频地址：
https://edu.csdn.net/course/detail/28645
搜索文档树find_all方法-keyword参数
keyword参数
文档内容如下：
html_doc = “”"
The Dormouse's story
Once upon a time there were three little sisters; and their names were Elsie, Lacie and Tillie; and they lived at the bottom of a well.
...
"""如果一个指定名字的参数不是搜索内置的参数名,搜索时会把该参数当作指定名字tag的属性来搜索,如果包含一个名字为 id 的参数,Beautiful Soup会搜索每个tag的”id”属性。
使用多个指定名字的参数可以同时过滤tag的多个属性: