Activate browser mode with doctype

Contemporary web browsers implement a variety of different engine modes in order to handle web pages authored according to web standards and those authored according to older practices that prevailed in the late 1990s. This article explains what those patterns are and how to trigger them.

Original text: Activating Browser Modes with Doctype by Henri Sivonen

Document scope

The mode switching included in this article applies to Firefox and other Gecko-based browsers, Safari, Chrome and other Webkit-based browsers, Opera, Konqueror, Internet Explorer for Mac, Internet Explorer for Windows, and IE embedded browsers. device. Avoid mentioning the name of the browser engine and instead use the name of the most well-known browser for that engine.

This article focuses on the mode selection mechanism rather than documenting the exact behavior of each mode.

model

Here are the various modes:

Mode with content type text/html

The mode selection for text/html content depends on doctype sniffing ( discussed later in this article ). In IE8, the mode depends on other factors as well. However, by default in IE8, the mode for non-intranet sites that are not on Microsoft's blacklist depends on the document type.

It cannot be overemphasized that the precise behavior of patterns differs in each browser, even though it is discussed uniformly in this article.

Quirks Mode

In quirks mode, the browser violates contemporary Web formatting specifications in order to avoid "breaking" pages that were created based on older practices that prevailed in the late 1990s. Different browsers implement different quirks. In Internet Explorer 6, 7, and 8, quirks mode effectively freezes IE 5.5. In other browsers, quirks mode is a small deviation from an almost standard mode.

If you are creating a new web page, you should comply with relevant specifications (especially CSS2.1) and use standards mode.

Standards Mode

In standards mode, the browser attempts to give standards-conforming documents as standard-correct processing as possible in a given browser.

Different browsers follow different phases, so standards mode is not a single goal.

HTML5 calls this mode "no quirks mode"

Almost Standards Mode

irefox, Safari, Chrome, Opera (starting from 7.5) and IE8 also have a mode called "almost standard mode", which implements the vertical size of table cells according to traditional methods rather than strictly following the CSS2 specification. Mac IE5, Windows IE6 and 7, versions prior to Opera 7.5, and Konqueror do not need almost standards mode because they at least do not strictly follow the CSS2 specification to implement table cell vertical dimensions in their respective standards modes. In fact, their standards mode is closer to Mozilla's Almost Standards mode than Mozilla's Standards mode.

HTML5 calls this mode "limited quirks mode".

IE7 mode

IE8 has a mode that freezes a copy of IE7's standards mode. Other browsers do not have a mode like this, and it is not specified by HTML5.

Mode with content type application/xhtml+xml (XML mode)

In Firefox, Safari, Chrome and Opera, the application/xhtml+xml HTTP content type (not a meta element nor a doctype!) triggers XML mode. In XML mode, the browser attempts to give the XML document specification-correct processing to the extent specified in the browser.

E6, 7 and 8 do not support application/xhtml+xml, nor does Mac IE5.

In the WebKit-based Nokia S60 browser, the application/xhtml+xml HTTP content type cannot trigger XML mode because the concern in mobile walled gardens is compatibility with non-standard content. ( Older "mobile browsers" can't use real XML parsers because non-canonical content is already tagged as XML.)

Without testing Konqueror enough, I can't say exactly what will happen in this browser.