This is a re-post from David Baron’s blog. This feature has landed in Mozilla Central (trunk) and only available with a Firefox Nightly Build for the time being.

Last night I landed support for :-moz-any() selector grouping. This allows providing alternatives between combinators, rather than having to repeat the entire selector for once piece that’s different. For example, it allowed replacing this rule in our user-agent style sheet:

/* 3 deep (or more) unordered lists use a square */ ol ol ul, ol ul ul, ol menu ul, ol dir ul, ol ol menu, ol ul menu, ol menu menu, ol dir menu, ol ol dir, ol ul dir, ol menu dir, ol dir dir, ul ol ul, ul ul ul, ul menu ul, ul dir ul, ul ol menu, ul ul menu, ul menu menu, ul dir menu, ul ol dir, ul ul dir, ul menu dir, ul dir dir, menu ol ul, menu ul ul, menu menu ul, menu dir ul, menu ol menu, menu ul menu, menu menu menu, menu dir menu, menu ol dir, menu ul dir, menu menu dir, menu dir dir, dir ol ul, dir ul ul, dir menu ul, dir dir ul, dir ol menu, dir ul menu, dir menu menu, dir dir menu, dir ol dir, dir ul dir, dir menu dir, dir dir dir { list-style-type: square; }

with this one:

/* 3 deep (or more) unordered lists use a square */ :-moz-any(ol, ul, menu, dir) :-moz-any(ol, ul, menu, dir) ul, :-moz-any(ol, ul, menu, dir) :-moz-any(ol, ul, menu, dir) menu, :-moz-any(ol, ul, menu, dir) :-moz-any(ol, ul, menu, dir) dir { list-style-type: square; }

In theory, I could even have used:

/* 3 deep (or more) unordered lists use a square */ :-moz-any(ol, ul, menu, dir) :-moz-any(ol, ul, menu, dir) :-moz-any(ul, menu, dir) { list-style-type: square; }

but this would have been slower since it no longer falls into the tag bucket. (If :-moz-any() turns out to be popular, we could add extra code so it’s just as fast, but I haven’t done so yet.)

:-moz-any() is allowed to contain selectors with multiple simple selectors (using the css3-selectors definition of simple selectors, not the CSS 2.1 definition), but it is not allowed to contain combinators or pseudo-elements. So you can write :-moz-any(p.warning.new, p.error, div#topnotice) or :-moz-any(:link, :visited).external:-moz-any(:active, :focus) , but you can’t put “ div p ” or “ div > p or “ :first-letter ” inside :-moz-any() .

This has a -moz- prefix for two reasons. First, it’s just a proposal, and hasn’t made its way into any specification. And second, it isn’t quite ready for prime-time, though, since it doesn’t yet handle specificity correctly.

Note: This will be extremely valuable in an HTML5 context when it comes to sections and headings. Since section , article , aside , and nav can be nested, doing something like styling all h1 elements at different depths could be extremely complex.

/* Level 0 */ h1 { font-size: 30px; } /* Level 1 */ section h1, article h1, aside h1, nav h1 { font-size: 25px; } /* Level 2 */ section section h1, section article h1, section aside h1, section nav h1, article section h1, article article h1, article aside h1, article nav h1, aside section h1, aside article h1, aside aside h1, aside nav h1, nav section h1, nav article h1, nav aside h1, nav nav h1, { font-size: 20px; } /* Level 3 */ /* ... don't even think about it*/

With -moz-any():

/* Level 0 */ h1 { font-size: 30px; } /* Level 1 */ -moz-any(section, article, aside, nav) h1 { font-size: 25px; } /* Level 2 */ -moz-any(section, article, aside, nav) -moz-any(section, article, aside, nav) h1 { font-size: 20px; } /* Level 3 */ -moz-any(section, article, aside, nav) -moz-any(section, article, aside, nav) -moz-any(section, article, aside, nav) h1 { font-size: 15px; }