Opera Browser Wiki : OperaQuirksMode

Opera Quirks Mode

Presto, the new rendering engine from Opera, has created a quirks mode to 'emulate' buggy rendering of pages common among older browsing software. This is triggered by the DocType of the HTML page.

The final version of Opera has followed an IE-bug in that if you have anything other than <DOCTYPE...> on the first line of your page (e.g. you have a standards-compliant <xml...> declaration) then the browser uses quirks mode. This will change in future releases. This has been fixed in Opera V7.1

off = quirks mode / on = standards mode

Label	Definition	with URL	without URL
Label	Definition	with URL	without URL
No !DOCTYPE		Off	Off
HTML (No Version)		Off	Off
HTML 2.0		Off	Off
HTML 3.0		Off	Off
HTML 3.2		Off	Off
HTML 4.0	No Definition	On	On
HTML 4.0	Frameset	On	Off
HTML 4.0	Transitional	On	Off
HTML 4.0	Strict	On	On
XHTML	All	On	On
XML		On	On
Unrecognized !DOCTYPE		On	On

To test whether Opera is in quirks or standard rendering mode, type the following into the address bar (or make it a bookmark):

javascript:alert(document.compatMode);

You should get an alertbox with the string "BackCompat" or "QuirksMode" if OperaQuirksMode is in effect, and "CSS1Compat" if Standards mode is in effect.

Note that the DOCTYPE switch only applies to HTML: XHTML pages served with the MimeTypes? "application/xhtml+xml", "application/xml", or "text/xml" will always be rendered in Standards mode, even if no DOCTYPE is used. There is an unofficial MimeType "text/xhtml" -- If a page is served with this MimeType, it must have a valid DOCTYPE for it to be rendered in Standards mode.

There *is* a DOCTYPE switch override in Opera 7.0, note however it is currently buggy (e.g. trying a standards override with NO DocType will still yield Quirks mode etc.)
Put this in your Opera6.ini under [User Prefs]:

CompatMode Override

If set to either 1 or 2 the switching mechanism is overridden as follows:

1. - Always Quirks Mode
2. - Always Standards Mode

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Behaviours known to be exhibited in Quirks mode:

• Colors not beginning with # accepted.
• Unitless numbers are interpreted as px (pixels).
• Opera 7.0 becomes case-insensitive for CSS class and ID selectors.
• CSS size and position properties with a space between the number and the unit accepted.
• CSS class and ID selectors starting with a number are allowed.
• The HTML 'tr' element doesn't have a 'height' attribute. Opera allows this attribute in Quirks Mode.
• Width property includes border-width and padding (MS Box Model - Opera 7 actually implements CSS3 declarations to switch box model (see here), and does so automatically in quirks mode)
• The CSS properties 'margin-left' and 'margin-right' are subtracted from the width of containing box when computing percentage widths.
• Font-size:small = default font size.
• Inline elements with a specified width are replaced by an inline block.
• CSS properties fail to be inherited into tables.
• Overflow:visible expands the box instead of allowing the content to flow outside it's dimensions (e.g. see here for an example page with no DocType declaration)

Behaviours that should change in Quirks mode:

• The :hover pseudo-element should be applied as if it was a:hover in quirks mode (stops badly coded CSS that uses :hover in style-sheets). *:hover should keep working as expected (do not take this literally: the universal selector does not work with :hover in Opera due to a bug; interpret this hint as a wildcard for any type selector).

References

• Opera7CSSIssues
• Opera 7 DocType Documentation
• CSSWiki:QuirksRenderingMode - The CSS wiki page on quirks mode
• IE Quirks information
• Mozilla Quirks information

Categories

CategoryOpera
CategoryTechnical

Backlinks

1. Opera7
2. Opera7CSSIssues
3. Opera7FixedCSSBugs
4. OperaQuirksMode

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