Bug 224811 – Implement CSS Lists counter-reset: reversed(list-item) and <ol>/<ol reversed> default style per spec

• Status: NEW
• Component: Layout and Rendering

[Simon Pieters (:zcorpan)]

The CSS Lists spec, with the reversed() proposal, is able to "explain" rendering of <ol> and <ol reversed> counters through presentational hints. See these spec changes:

https://github.com/whatwg/html/pull/4816
https://github.com/w3c/csswg-drafts/pull/6096

and wpt tests:

https://github.com/web-platform-tests/wpt/pull/28040
https://github.com/web-platform-tests/wpt/pull/28453

[Radar WebKit Bug Importer]

<rdar://problem/77206733>

[Karl Dubost]

https://wpt.fyi/results/css/css-lists/css-lists-no-interpolation.html
https://wpt.live/css/css-lists/css-lists-no-interpolation.html

[Karl Dubost]

 Chrome ships it. 
Firefox ships it.

https://drafts.csswg.org/css-lists/#valdef-counter-reset-reversed-counter-name

1. Parsing: Source/WebCore/css/parser/CSSPropertyParserConsumer+Lists.cpp needs a reversed(<counter-name>) function branch alongside the bare ident path.
2. Data model: CounterDirectives (Source/WebCore/rendering/style/CounterDirectives.h) is currently just std::optional<int>  resetValue/incrementValue/setValue. It needs a flag for "this reset is reversed" so resolution knows to count downward.
3. Style serialization: StyleCounterReset (Source/WebCore/style/values/lists/StyleCounterReset.{h,cpp}) and computed style getters need to round-trip the reversed() notation.
4. Counter resolution: RenderCounter.cpp needs to compute the implicit start (= count of incremented descendants when the value is omitted) and decrement instead of increment.
5. UA sheet: html.css for ol[reversed] should use counter-reset: reversed(list-item) <start> and counter-increment: list-item -1, replacing the current behavior.