Problem with DOCTYPE_html/css_WEB-ITnose

The DOCTYPE statement on Baidu's homepage is:
It declares that it does not specify which DTD to use, nor does it specify the address. So which DTD will the browser use?
In addition, in this case, why does the browser still follow the standards mode for rendering?

Thank you!

Reply to discussion (solution)

Not specified. The default standards adopted by each browser may be different. Some page function styles, etc. may be wrong

Not specified. The default standards adopted by each browser may be different. Some page functions and styles may be wrong
Then why doesn’t Baidu specify it?

HTML5 declaration method.

http://www.w3school.com.cn/html5/html5_doctype.asp

Oh okay, thank you!