¿Qué causa que Internet Explorer entre en modo peculiaridades?

What causes Internet Explorer to go into quirks mode?

Anything before the DOCTYPE, like a comment or an XML declaration will trigger quirks mode in Internet Explorer 9 and older. In HTML5, the only purpose of the DOCTYPE is to activate full standards mode.

The reason we can’t just generalize when to open a link in a new browser tab (or window) versus keep users in the same browser tab is because our user’s needs, expectations, and reactions aren’t triggered by a file format or link type (internal or external).

If you navigate to sites on your local intranet like http://myPortal and http://sharepoint/sites/mySite , Internet Explorer 8 identifies itself with a User Agent string of ‘7’, Version Vector of ‘7’, and displays webpages that trigger standards mode in Internet Explorer 7 Standards mode.

There are “Internet Explorer 8”, “Internet Explorer 8 Compatibility Mode”, and IE7 mode in IE8. However, the default setting in IE make all intranet website use “IE8 Compatibility Mode” even I have setted doctype, the meta tag, http header as suggested to force it into IE8 mode.

Quirks mode. Jump to navigation Jump to search. In computing, quirks mode refers to a technique used by some web browsers for the sake of maintaining backward compatibility with web pages designed for Internet Explorer 5 and earlier, instead of strictly complying with W3C and IETF standards in standards mode.

In HTML5, the only purpose of the DOCTYPE is to activate full standards mode. Older versions of the HTML standard gave additional meaning to the DOCTYPE, but no browser has ever used the DOCTYPE for anything other than switching between quirks mode and standards mode. See also a detailed description of when different browsers choose various modes.

In full standards mode, the behavior is (hopefully) the behavior described by the HTML and CSS specifications. In almost standards mode, there are only a very small number of quirks implemented. How do browsers determine which mode to use?