A document
is always set to one of three modes:
- no-quirks mode, the default;
- quirks mode, used typically for legacy documents;
- limited-quirks mode.
The mode is
only ever changed from the default if the document is created by the HTML
parser, based on the presence, absence, or value of the DOCTYPE string. [HTML]
No-quirks
mode was originally known as "standards mode" and limited-quirks mode
was once known as "almost standards mode". They have been renamed
because their details are now defined by standards. (And because Ian Hickson
vetoed their original names on the basis that they are nonsensical.)
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Quirks Mode
In the
Quirks mode, browsers violate contemporary Web format specifications in order
to avoid “breaking” pages authored according to practices that were prevalent
in the late 1990s.
Standards
Mode
In the
Standards mode, browsers try to give conforming documents the
specification-wise correct treatment to the extent implemented in a particular
browser. HTML5 calls this mode the “no quirks mode.”
Almost
Standards Mode
Firefox,
Safari, Chrome, Opera (since 7.5) and IE8 also have a mode known as “Almost
Standards mode,” that implements the vertical sizing of table cells
traditionally and not rigorously according to the CSS2 specification. HTML5
calls this mode the “limited quirks mode.”
Possible Impacts:
- In some browsers, the box model
changes to the IE 5.5 version of the box model in quirks mode.
- Some browsers don't inherit
styles into tables
- Quirks mode affects the parsing
of CSS and CSS layout dramatically, if you are converting pages to
standards mode from quirks mode, be sure to test your CSS layout and
parsing extensively.
- Watch for changes to scripting
when in quirks mode. Firefox changes the way the id-attribute works,
for example. IE8 and IE9 have very dramatic changes to scripting in quirks
mode.
These information are the result of a study I made while working in a legacy product, to understand the behavior why the browser was running under quirks/compatibility mode and find the best solution, considering possible impacts... I strongly recommend to use the latest doctype declaration (i.e. for HTML5) and replace deprecated CSS styles for the html5 equivalent ones).
References:
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