Intent to Ship: CSS Root Font Units: 'rex', 'rch', 'ric', 'rlh'

[Daniil Sakhapov]

Contact emails

sakh...@chromium.org

Specification

https://www.w3.org/TR/css-values-4/#font-relative-lengths

Summary

Allows usage of root font units. Currently only 'rem' is supported in Blink. This feature supports root element variants of ex, ch, ic, and lh too.

Blink component

Blink>CSS

Search tags

rlh, ric, rch, rex, root font

TAG review

The feature is not fundamental and only implements an existing standard

TAG review status

Not applicable

Risks

Interoperability and Compatibility

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/725)

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/112)

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

no

Debuggability

The new units should be automatically supported by devtools. No need for any changes.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

https://wpt.fyi/css/css-values/rlh-invalidation.html

https://wpt.fyi/css/css-values/ric-invalidation.html

https://wpt.fyi/css/css-values/rch-invalidation.html

https://wpt.fyi/css/css-values/rex-invalidation.html

https://wpt.fyi/css/css-values/lh-rlh-on-root-001.html
https://wpt.fyi/css/css-typed-om/stylevalue-subclasses/numeric-objects/cssUnitValue.html

https://wpt.fyi/css/css-contain/container-queries/font-relative-units.html

https://wpt.fyi/css/css-contain/container-queries/font-relative-units-dynamic.html

Flag name

#enable-experimental-web-platform-features / CSSNewRootFontUnits (Blink)

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=1381037

Estimated milestones

DevTrial on desktop

111

DevTrial on Android

111

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5073969265246208

[Mike Taylor]

On 1/5/23 5:07 AM, 'Daniil Sakhapov' via blink-dev wrote:

Contact emails

sakh...@chromium.org

Specification

https://www.w3.org/TR/css-values-4/#font-relative-lengths

Summary

Allows usage of root font units. Currently only 'rem' is supported in Blink. This feature supports root element variants of ex, ch, ic, and lh too.

Blink component

Blink>CSS

Search tags

rlh, ric, rch, rex, root font

TAG review

The feature is not fundamental and only implements an existing standard

Note that CSS Values and Units Level 4 is not yet a standard, but a working draft.

That said, it seems the TAG recently reviewed the draft spec and was satisfied with it:

https://github.com/w3ctag/design-reviews/issues/781

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[Philip Jägenstedt]

I see the Gecko issue has now been resolved as positive, which is great.

Are any of these units already supported in Firefox or Safari, or would we be the first to ship all of them? (I took a look at one test and have a guess, but just as well to ask.)

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/925d0226-4c69-1c28-13b1-59854c1617ca%40chromium.org.

[Daniil Sakhapov]

Safari has claimed to implement rlh, but nothing else I guess. None of them are in Firefox.

[Philip Jägenstedt]

I see, thanks for checking that! It’s worth checking that our test results match other browsers who have implemented, in case they can reveal different choices or interpretations of the spec.

LGTM1

[Rick Byers]

LGTM2

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAARdPYe8h2RHvZgHHsZ5xdrx8sKbhgSamZof6xkq2p9qV8Bobw%40mail.gmail.com.

[Mike Taylor]

LGTM3