Notes on Mozilla Quirks Mode

The following change exist between Mozilla's standards mode and quirks mode: (XXX add links to description)

• Miscellaneous & Style
  • All of the style rules in quirk.css apply.
  • The CSS parser accepts colors not beginning with #.
  • The CSS parser interprets unitless numbers as px (except for font-size because that was what Nav4 did, and except for line-height and any other properties where they have distinct meaning).
  • HTML colors are parsed differently (# is not required, and missing digits are filled int differently)
  • An empty string for the background attribute sets the background URL to empty only in quirks mode.
  • System fonts work differently in navquirks mode (shouldn't the form controls that use them be the ones working differently instead?).
  • HTML (1-7) and CSS (xx-small - xx-large) font sizes are calculated slightly differently (see bug 18136).
  • For bug 18817, quirks mode was intended to accept stylesheets in certain cases when strict mode did not, but the code has since gotten somewhat mangled and doesn't seem to have much point anymore.
• Block and Inline layout
  • Line height (not line-height) calculations are different to fix bug 5821 and bug 24186 (some other issues are described in bug 22274).
  • There are a bunch of quirks to get percentage heights on images and tables to "work" (the way they did in Nav4), some of which may cause other effects (see bug 54119).
  • The HR element is treated differently in quirks and strict mode (and arguably wrong in both).
• Tables
  • Table background colors work differently (see bug bug 4510) It is not clear that this quirk is needed.
  • In quirks mode absmiddle (handled incorrectly?) and middle (perhaps incorrectly as well?) are accepted as values of align on table cells, and absmiddle, abscenter, and middle are supported on tables (treated the same as center).
  • TD, TH, TR, THEAD, TBODY, and TFOOT elements have the document background (and color?) applied to them (when the document background is specified in certain ways?) (see also bug 70831 ).
  • The empty-cells property defaults to hide in quirks mode but show (according to CSS2 errata) in strict mode (see bug 33244) (though the correct fix would be to specify it on the HTML TABLE element in quirk.css).
  • In quirks mode floated tables never move to the next "line" if they don't fit next to other floats, they just keep widening the page (see bug 43086).
  • In quirks mode colspan="0" and rowspan="0" are intentionally not handled as described in HTML4.
  • hspace and vspace are supported on TABLE only in quirks mode.
  • In quirks mode, when tables have a border style of inset or outset, the border color is based on the background color of the table or of the nearest ancestor with non-transparent background.
  • In quirks mode table cells with a border have a minimum width of one pixel.
  • The basic table layout strategy ignores padding (on what) in quirks mode.
  • The basic table layout strategy handles widths differently in some way.
• Forms
  • Button inputs calculate their size differently.
  • In standard mode a BUTTON element (?) can submit only if it lacks a type attribute.
  • Text inputs (and other form controls containing text???) calculate their size differently (see bug X for the description of the original fix and also bug X for suggested modifications)
  • The fonts for button INPUT elements and SELECT elements are computed differently.
  • The requirement of HTML that one button in a radio group is always selected (by default) is not enforced in quirks mode.
• Frames
  • In quirks mode marginwidth and marginheight on a FRAME are propagated to the contained BODY.
  • In a frame size specification 0* is treated as 1* (see bug 40383).
  • The scrolling attribute on FRAME is handled differently.

(Back to Mozilla Stuff, David Baron)

LDB, dbaron@dbaron.org, 2001-06-06