Intent to Ship: CSS Pseudo Element ::backdrop inheriting from Originating Element

Rune Lillesveen

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Jan 9, 2024, 6:50:56 AMJan 9

to blink-dev

Contact emails

fut...@chromium.org

Explainer

None

Specification

https://drafts.csswg.org/css-position-4/#backdrop

Summary

The ::backdrop pseudo element used to inherit from initial values. That meant ::backdrop could not use custom property values unless specified directly on the ::backdrop rule. The specification has now changed so that ::backdrop inherits from the originating element, and with that the implementation.

Blink component

Blink>CSS

TAG review

None

TAG review status

Not applicable

Risks

Interoperability and Compatibility

A compatibility risk is that existing content may rely on inheriting initial values. For instance, this rule may change from having a backdrop with the initial foreground color to using the color property of the originating element: ::backdrop { background: currentColor } Interop risk is low for shipping since Firefox and Safari already do ship.

Gecko: Shipped/Shipping (https://bugzilla.mozilla.org/show_bug.cgi?id=1855668) Shipped in Firefox 120

WebKit: Shipped/Shipping (https://bugs.webkit.org/show_bug.cgi?id=263834)

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?

None

Debuggability

N/A

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

Yes

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

Yes

https://wpt.live/css/css-position/backdrop-inherit-computed.html https://wpt.live/css/css-position/backdrop-inherit-rendered.html

Flag name on chrome://flags

#enable-experimental-web-platform-features

Finch feature name

BackdropInheritOriginating

Requires code in //chrome?

False

Tracking bug

https://crbug.com/827397

Estimated milestones

Shipping on desktop	122
DevTrial on desktop	119

Shipping on Android	122
DevTrial on Android	119

Shipping on WebView

122

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

None

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/4875749691752448

This intent message was generated by Chrome Platform Status.

--

Rune Lillesveen

Rick Byers

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Jan 10, 2024, 10:42:16 AMJan 10

to Rune Lillesveen, blink-dev

Given how trivial and niche this is and that WebKit and Gecko have both shipped this without any apparent compat fallout, I agree the compat risk is very low. I'm ok treating it as a bugfix, but please circle back here (and consider using your killswitch) if you hear of any breakage in practice. LGTM1 to ship.

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Daniel Bratell

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Jan 10, 2024, 10:46:32 AMJan 10

to Rick Byers, Rune Lillesveen, blink-dev

LGTM2

/Daniel

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFUtAY-8sefA9ZJh5q0cDnqRjUAcaBBM_wEVw0DLvHiqYErCtw%40mail.gmail.com.

Manuel Rego Casasnovas

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Jan 10, 2024, 11:01:17 AMJan 10

to Daniel Bratell, Rick Byers, Rune Lillesveen, blink-dev

LGTM3.

BTW, one question about pseudo-elements, for some of them we have use
counters buts not for all (like this one, or at least I didn't find it).
Is that fine? Or should we usually add use counters for new pseudo-elements?

Cheers,
Rego

>> <https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3ECSS>

>>
>>
>> TAG review
>>
>> None
>>
>>
>> TAG review status
>>
>> Not applicable
>>
>>
>> Risks
>>
>>
>>
>> Interoperability and Compatibility
>>
>> A compatibility risk is that existing content may rely on
>> inheriting initial values. For instance, this rule may change from
>> having a backdrop with the initial foreground color to using the
>> color property of the originating element: ::backdrop {
>> background: currentColor } Interop risk is low for shipping since
>> Firefox and Safari already do ship.
>>
>>
>>

>> /Gecko/: Shipped/Shipping

>> (https://bugzilla.mozilla.org/show_bug.cgi?id=1855668) Shipped in
>> Firefox 120
>>

>> /WebKit/: Shipped/Shipping
>> (https://bugs.webkit.org/show_bug.cgi?id=263834)
>>
>> /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?
>>
>> None
>>
>>
>>
>> Debuggability
>>
>> N/A
>>
>>
>>
>> Will this feature be supported on all six Blink platforms
>> (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?
>>
>> Yes
>>
>>
>> Is this feature fully tested by web-platform-tests

>> <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?

>> <https://chromestatus.com/>.

>>
>> --
>> Rune Lillesveen
>>
>> --
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>> To unsubscribe from this group and stop receiving emails from it,
>> send an email to blink-dev+...@chromium.org.
>> To view this discussion on the web visit

>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACuPfeRpWk%2BOh_g1LD7wUwXk7L1Agu%2Bd84Myk8uCkZQy_-S35g%40mail.gmail.com <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACuPfeRpWk%2BOh_g1LD7wUwXk7L1Agu%2Bd84Myk8uCkZQy_-S35g%40mail.gmail.com?utm_medium=email&utm_source=footer>.

>>
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>> To view this discussion on the web visit

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>
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Rune Lillesveen

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Jan 15, 2024, 4:34:00 AMJan 15

to Manuel Rego Casasnovas, Daniel Bratell, Rick Byers, blink-dev

On Wed, Jan 10, 2024 at 5:01 PM Manuel Rego Casasnovas <re...@igalia.com> wrote:

LGTM3.

BTW, one question about pseudo-elements, for some of them we have use
counters buts not for all (like this one, or at least I didn't find it).
Is that fine? Or should we usually add use counters for new pseudo-elements?

We should add counters for new pseudo elements.

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Rune Lillesveen

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