Mode problem triggered by DOCTYPE under IE8_html/css_WEB-ITnose

Many places say that the statement will turn on the standards mode, and I have seen that Google and Baidu do this. But I found that my program is different. When I press F12 under ie8, I see that the browser mode is IE8 Compat View, and the Document Mode is IE7 Standard. I reset them to IE8 standards mode, then restarted the browser, and came back to find that they had changed back again. Of courseI tried , also IE8 Compat View/IE7 Standard.
Tested under operating systems XP and Win7.

I would like to ask why the browser mode I want cannot be IE8 and the document mode is Ie8 standard? What factors affect it?

Reply to discussion (solution)

Shouldn’t browser mode and document mode be controlled in this way:

I further found that when testing locally, if you use http://localhost to access it, it will be in ie8 standard mode, and use http://ipAddress to access it. If so, it is ie7 mode, please explain.

Shouldn’t browser mode and document mode be controlled in this way:

I have tested your suggestion and it works.

requires a browser that supports html5.
For specific information, please see http://www.w3school.com.cn/html5/html5_doctype.asp

Quoting the reply from huanghui8030 on the 1st floor: This method should not be used in browser mode and document mode. To control:

I have tested your suggestion and it works. Give points if it's useful.

Does not need to support HTML5 It has been around a long time ago, much earlier than 5

Does not need to support HTML5 < !doctype html>It existed a long time ago, much earlier than 5
In non-html5 environments, DTD needs to be referenced
If dtd is not referenced, different browsers may use different specifications to parse web pages.
html5 uses unified standards