Intent to Ship: Sec-CH-Prefers-Reduced-Transparency User Preference Media Features Client Hints Header

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Luke

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Aug 30, 2023, 4:55:52 PM8/30/23
to blin...@chromium.org

Contact emails

lukewa...@gmail.comlu...@warlow.dev

Explainer

https://github.com/wicg/user-preference-media-features-headers/blob/main/README.md

Specification

https://wicg.github.io/user-preference-media-features-headers/#sec-ch-prefers-reduced-transparency

Summary

User Preference Media Features Client Hints Header defines a set of HTTP Client Hints headers around user preference media features as defined by Media Queries Level 5. If used as Critical Client Hints, these headers allow servers to make smart choices regarding, e.g., CSS inlining. Sec-CH-Prefers-Reduced-Transparency reflects the user's prefers-reduced-transparency preference.



Blink component

Blink>CSS

Search tags

client hintssec-ch-prefers-reduced-transparencyprefers-reduced-transparency

TAG review



TAG review status

Pending

Risks



Interoperability and Compatibility



Gecko: No signal (https://github.com/mozilla/standards-positions/issues/526)

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/15)

Web developers: Positive (WICG proposal Issue: https://github.com/WICG/proposals/issues/30 with feedback from developers working for Facebook and Magento. Twitter: https://twitter.com/kilianvalkhof/status/1392404416335056896. The proposal was initially discussed in https://github.com/w3c/csswg-drafts/issues/4162 and received positive feedback via 18 Likes)

Other signals:

Activation

Developers will include Sec-CH-Prefers-Reduced-Transparency in the response headers Accept-CH and Critical-CH to let the browser know that they’re interested in the user's transparency preferences. If supported, the request header Sec-CH-Prefers-Reduced-Transparency will be populated with the appropriate value. This follows the same pattern as existing Preference Client Hints and as such should be easy for developers to make use of.



Security

This feature could be used for fingerprinting as it exposes a user preference. However, this is already exposed to CSS/JS by the `prefers-reduced-transparency` media query.



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?



Debuggability

Developers can change this client hint header value by emulating prefers-reduced-transparency via Devtools in the Rendering Panel.



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

Yes

The feature will be supported on all platforms, but whether the user will be able to signal a reduced transparency preference depends on the OS.



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

Yes

Flag name on chrome://flags

#enable-experimental-web-platform-features

Finch feature name

ClientHintsPrefersReducedTransparency

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=1466423

Sample links


https://sec-ch-prefers-reduced-transparency.glitch.me

Estimated milestones

Shipping on desktop118
DevTrial on desktop118
Shipping on Android118
DevTrial on Android118


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).



Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6242983812268032

Links to previous Intent discussions

Intent to prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/B1ED49A6-31BF-4D28-89B3-D2973F9F12DA%40gmail.com

This intent message was generated by Chrome Platform Status.

Mike Taylor

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Sep 1, 2023, 6:10:25 PM9/1/23
to Luke, blin...@chromium.org

On 8/30/23 3:55 PM, Luke wrote:

Contact emails

lukewa...@gmail.comlu...@warlow.dev

Explainer

https://github.com/wicg/user-preference-media-features-headers/blob/main/README.md

Specification

https://wicg.github.io/user-preference-media-features-headers/#sec-ch-prefers-reduced-transparency

Summary

User Preference Media Features Client Hints Header defines a set of HTTP Client Hints headers around user preference media features as defined by Media Queries Level 5. If used as Critical Client Hints, these headers allow servers to make smart choices regarding, e.g., CSS inlining. Sec-CH-Prefers-Reduced-Transparency reflects the user's prefers-reduced-transparency preference.



Blink component

Blink>CSS

Search tags

client hintssec-ch-prefers-reduced-transparencyprefers-reduced-transparency

TAG review

Anything relevant to link here?
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Luke

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Sep 1, 2023, 7:06:25 PM9/1/23
to blink-dev, mike...@chromium.org, Luke
Apologies, https://github.com/w3ctag/design-reviews/issues/632 would be the relevant link. Will update in Chromestatus too.

Yoav Weiss

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Sep 6, 2023, 11:25:48 AM9/6/23
to Luke, blink-dev, mike...@chromium.org

Mike Taylor

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Sep 6, 2023, 11:34:16 AM9/6/23
to Yoav Weiss, Luke, blink-dev

LGTM2

Chris Harrelson

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Sep 6, 2023, 11:54:12 AM9/6/23
to Mike Taylor, Yoav Weiss, Luke, blink-dev
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