Intent to Ship: Selection API getComposedRanges and direction
Di Zhang
Specification
Summary
This feature ships two new API methods for the Selection API: * Selection.direction which returns the selection's direction as either "none", "forward" or "backward" * Selection.getComposedRanges() which returns a list of 0 or 1 “composed” StaticRange A “composed” StaticRange is allowed to cross shadow boundaries, which normal Ranges cannot. For example: const range = getSelection().getComposedRanges({ shadowRoots: [root] }); If the selection crosses a shadow root boundary that isn’t provided in the shadowRots list, then the StaticRange's endpoints will be “rescoped” to be outside that tree. This makes sure we do not expose unknown shadow trees.
Blink component
TAG review status
Risks
Interoperability and Compatibility
None
Gecko: Positive (https://github.com/mozilla/standards-positions/issues/1055) Currently in development. https://groups.google.com/a/mozilla.org/g/dev-platform/c/zF7soLapT-Y
WebKit: Shipped/Shipping (https://github.com/WebKit/WebKit/pull/10843#issuecomment-1592149737) Partially shipped new API
Web developers: Positive (https://stackoverflow.com/questions/62054839/shadowroot-getselection)
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, this is only shipping new APIs without modifying existing behavior.
Debuggability
None
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?Yes
The Selection API is supported on all platforms.
Is this feature fully tested by web-platform-tests?Yes
Tests can be found at https://wpt.fyi/results/selection/shadow-dom/tentative?label=experimental&label=master&aligned
Flag name on about://flags
Finch feature name
Requires code in //chrome?
Tracking bug
Adoption expectation
Adoption plan
Estimated milestones
Shipping on desktop
137
Shipping on Android
137
Shipping on WebView
137
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).
This new API is important to return Selection endpoints that are inside a shadow DOM and currently not accessible by API. This depends on new specification definitions of what it means to have a range that is composed and how the endpoints should be compared. That specification includes tree traversal, boundary point comparisons and the specification language is quite complex. The specification PR has been open since Dec 17, 2024 and is stalling due to disagreement on how to phrase/word the spec. There are a few remaining open issues about this, but none of those should affect the shape of the API - they only affect the spec text itself.Links to previous Intent discussions
Daniel Clark
Looking at the WPT results, there are a lot of Safari failures despite them having already shipped this.
https://wpt.fyi/results/selection/shadow-dom/tentative?label=experimental&label=master&aligned
Do you have an understanding of what those gaps are, and whether there’s a path towards resolving them and ending up with interoperable implementations?
I am also wondering if there should be a TAG review for this. It seems that the spec is still somewhat in flux and the shipped WebKit implementation doesn’t align all that closely with Chromium’s given the WPT results, so I’m not sure this Intent quite meets the spirit of the exceptions for a TAG review. And in any case the TAG may be able to help unblock some of the disagreements that have caused the spec changes to stall out.
-- Dan
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Di Zhang
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Vladimir Levin
Mike Taylor
LGTM2
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Daniel Bratell
LGTM3
/Daniel
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