Intent to Ship: CSS scroll-boundary-behavior

[Yunjia (Sandra) Sun]

Intent to Ship: CSSOM scroll-boundary-behavior

Contact emails

suny...@chromium.org, maj...@chromium.org

Spec

https://wicg.github.io/scroll-boundary-behavior/

Summary

CSS scroll-boundary-behavior allows developers to determine the browser's behavior once a scroller has reached its full extent. The unused delta can be propagated to the parent causing scroll chaining, create a glow/bounce effect without chaining, or just get consumed silently. In particular when used on viewport defining element, it controls if overscroll can be used for navigations actions such as pull-to-refresh or swipe navigations. This standardizes a supercharged version of "-ms-scroll-chaining".

scroll-boundary-behavior: auto | contain | none

• auto: propagate scroll to the parent scroller. If there is no parent scroller (e.g., viewport) user-agent may perform a default action (e.g. navigation) or show any appropriate overscroll UI affordance. This is the default value.

• contain: do not propagate. The user agent may show an appropriate overscroll UI affordance such as bounce or glow.

• none: same as contain but also prevents any overscroll UI affordance e.g. bounce or glow.

There will be scroll-boundary-behavior-{x,y} long-hands to control each axis individually.

Link to “Intent to Implement” blink-dev discussion

Intent to Implement: CSS scroll-boundary-behavior

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

The scroll chaining behavior for inner scrollers is supported on all platforms. The behavior on the viewport to prevent overscroll navigations is currently supported on Android for pull-to-refresh, and we are working to support it on Mac and Chrome OS for swipe navigation.

Interoperability and Compatibility Risk

Edge: Public support

Firefox: Public support

Safari: No signals

Web developers: Positive (Facebook, AMP, numerous crbugs)

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

We currently have a layout test that are written using test-harness.js but depend on gpu benchmarking for automation. We have a plan to upstream them to a web-platform-test by refactoring our the automation.

OWP launch tracking bug

crbug.com/672921

Entry on the feature dashboard

https://www.chromestatus.com/features/5734614437986304

[Philip Jägenstedt]

Very nice to see prefixed properties in other engines (-ms-scroll-chaining) turning into standardized features!

Have you filed a TAG review request for this, and is there a WebKit bug tracking this?

This all seems very reasonable, with stronger-than-usual support from other vendors (Firefox in particular), so LGTM1 with those bugs filed.

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[Chris Harrelson]

LGTM2, with the same caveats as Philip. Glad to see this feature launch.

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[Majid Valipour]

Thanks for feedback. I went ahead and filed a TAG review request and a WebKit bug.

Majid

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[Rick Byers]

LGTM3

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[Majid Valipour]

FYI, there was a recent request to use a shorter name for 'scroll-boundary-behavior' CSS property. After some bikeshedding there is consensus on using 'overscroll-behavior'. We intend to change the name but are still targeting to ship the feature in M63. We will update all documentations to use the new name.

Majid

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[Chris Harrelson]

Still LGTM. :)

I'd say assume your feature is still approved unless another API owner raises a concern. Thanks for bringing this change to the community's attention!

Chris

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