What is quirks mode?

In a lot of articles about design, quirks mode is mentioned.
Anybody have an idea about this thing in plain text and in a development prospective?


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Method 1

you can read in this links




Modern browsers generally try to
render HTML content according to the
W3C recommendations. However, to
provide compatibility with older web
pages, and to provide additional
“intuitive” functionality, all
browsers support an alternative
“quirks mode”.

Quirks mode is not, however, a
standard. The rendering of any page in
quirks mode in different browsers may
be different. Whenever possible, it is
better to adhere to the W3C standards
and try and avoid depending on any
past or present browser quirks.

Generally, quirks mode is turned on
when there is no correct DOCTYPE
declaration, and turned off when there
is a DOCTYPE definition. However,
invalid HTML – with respect to the
chosen DOCTYPE – can also cause the
browser to switch to quirks mode.

More information on the different
quirks modes in different browsers can
be found at QuirksMode.org

Method 2

Quirks mode means your page is running without a document type declared, the document type is defined at the very top of a page and it denotes how the browser should read the HTML. This is StackOverflows doctype:


w3.org specifies web standards and document types, because Stack Overflow uses this doctype it must adhere to the specification of that doctype.

This is HTML 4.01 Strict DTD, which
excludes the presentation attributes
and elements that W3C expects to phase
out as support for style sheets
matures. Authors should use the Strict
DTD when possible, but may use the
Transitional DTD when support for
presentation attribute and elements is

Method 3

In past days when web browsers did not have full/correct implementations of CSS, developers relied on these idiosyncrasies to make their pages render properly. However, as browsers became more standards-compliant, these pages no longer rendered correctly, as they were written for what bascially was a different type of CSS. This is where quirks mode comes in, as it handles pages written for these broken CSS implementations.

So in 2009, you don’t really need to worry about quirks mode unless you’re handling older CSS, or older browsers. Just write your CSS to current web standards, and you be OK.

Method 4

Quirks mode also known as Compatibility Mode – means your page is running without a document type declared(this is old school, so this is most likely not needed anymore)
The whole point of quirks mode is that it’s a compatibility mode for IE5. This means that in addition to changing the layout mode, it also switches off most of the browser features that have been invented since IE5.
In quirks mode, the web browser attempts to render/make code based on a ‘best-guess’, this includes a generous interpretation of code that may be non-standard or poorly-formed.
if you don’t declare a doctype, the browser will have to guess what version of HTML/CSS you’re running
Quirks mode enables older HTML documents to still ‘work
its a technique used by web browsers to maintain backward compatibility with older webpages.

if you write a correct doctype, that will trigger standard mode and not Quirks mode
older browsers like Netscape 4, are permanently locked in quirks mode

Quirks mode enables your browser to behave as if it is an older browser

It’s a mode in which the browser is not law-abiding. It accepts any malformed mark-up in this mode and is not strict with syntax, tags and elements
basically means it’ll accept your code even if its not-correctly written

In quirks mode, browsers behave as they did in the early days of the web. This was done to prevent old sites from breaking too much in new browsers.

there is a difficulty in writing a page that looks the same in all browsers. In point of fact, that’s impossible. Many browsers were written with special features that only they could handle. Or they have special ways of handling things that are different from how other browsers handle them
Using a non-standard will cause every browser to run in quirks mode. But not all browsers behave the same in quirks mode, each browser reverts to its own unique rendering engine which is why it’s very difficult to get a page looking alike in different browsers.

also all your html5 css won’t work because it won’t be compatible

Quirks mode supports the JavaScript functionality of IE6, It is similar to the behavior of IE5 and the Quirks mode behavior of IE6, IE7 and IE8.

in quirks mode, document.body (the body-element) is the root element and in standard mode it’s the html-element (document.documentElement).
quirks mode is for the old rules of browsers, they made it so that old websites that were written before the world wide web came and before HTML5 was invented don’t break. so quirks mode is just to support those websites that had incorrect CSS features. so now developers had a choice. go with standard (todays browsers) or quirks mode for older browsers and websites. in quirks mode a lot of CSS/HTML features that we have today don’t work correctly.

Method 5


  • In quirks mode, the web browser attempts to render code based on a ‘best-guess’, this includes a generous interpretation of code that may be non-standard or poorly-formed.
  • A web browser may switch to quirks mode if a webpage has no document type declaration or has an incomplete document type declaration (for example, if the URI to the DTD is omitted).
  • Quirks mode enables older HTML documents to still ‘work’, and should be triggered when the code that has been used is known to fail contemporary technical standards (and when there is no intention/budget to revise legacy content).

Method 6

Trust my answer tested by me almost always, not its votes especially received from needless guys.

In addition to other answers, the mode can be checked by

javascript:window.alert('You are in ' + (document.compatMode==='CSS1Compat'?'Standards':'Quirks') + ' mode.')

What is quirks mode?

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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