!doctype HTML function

1.<! Doctype> is the instruction that the Web browser writes about which HTML version the page uses.

2.document.compatmode:

Backcompat: Weird mode, the browser uses its own weird mode to parse the rendered page.
Css1compat: Standard mode, browser uses the standard resolution rendering page.

By default, browsers render pages according to their own quirks, different browsers have different quirks, and the same code shows different results.

Declared the <! DOCTYPE Html> The browser will parse the rendered page according to the standard of the web, showing the same result.

3. There are three kinds of <! in HTML 4.01 Doctype> statement.

There is only one of the HTML5:<! DOCTYPE html>

!doctype HTML function