On Sat, Nov 8, 2025 at 12:59 AM Rick Byers <[email protected]> wrote:
> This has some risk of being a breaking change, right? How would
> you characterize that risk? Firefox having this is obviously a good sign,
> but any other data or arguments on the risk? I imagine SVG use is fairly
> rare, and any selector mismatch would most likely be a minor formatting
> issue, right?
>
An instantiated subtree will no longer be able to do selector matching
against the surrounding elements from where it was instantiated from.
In the following case, the use instance of the rect would no longer be red:
<!DOCTYPE html>
<style>
.original rect { fill: red; }
rect { fill: green; }
</style>
<svg>
<defs class="original">
<rect id="r" x="0" y="0" width="100" height="100" />
</defs>
<use href="#r"></use>
</svg>
I think this is unlikely to break real sites.
In order to use-count this, we would have to run both ways of cascading (or
at least selector matching) to detect such cases.
The main benefit from this change, I think, is that it fixes
https://crbug.com/40663285 which is about :hover and other state selector
matching which is currently broken in <use> instances.
On Fri, Nov 7, 2025 at 1:51 AM Philip Jägenstedt <[email protected]>
> wrote:
>
>> LGTM1
>>
>> The WebKit standards position was only filed yesterday, but this seems
>> straightforward and aligns with spec+Firefox, so I don't think we should
>> wait on it. In the unlikely event there is feedback, please ping this
>> thread.
>>
>> On Fri, Nov 7, 2025 at 9:44 AM Rune Lillesveen <[email protected]>
>> wrote:
>>
>>> *Contact emails*
>>> [email protected]
>>>
>>> *Specification*
>>> https://www.w3.org/TR/SVG2/struct.html#UseElement
>>>
>>> *Summary*
>>> Align the Blink implementation with the SVG2 specification for matching
>>> CSS rules in <use> element trees.
>>>
>>> Match selectors against the <use> instantiation elements instead of the
>>> originating element subtree. This means selectors will no longer match
>>> ancestor and sibling elements outside the cloned subtree. More importantly,
>>> state selectors like :hover will now start matching in <use> instances.
>>>
>>> *Blink component*
>>> Blink>SVG
>>> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ESVG%22>
>>>
>>> *Web Feature ID*
>>> Missing feature
>>>
>>> *Motivation*
>>> CSS selectors match against the wrong tree for <use> instantiations,
>>> which means selectors do not match correctly for structural relationships
>>> and user interaction state (see :hover issue that will be fixed shipping
>>> this feature: https://crbug.com/40663285)
>>>
>>> *Initial public proposal*
>>> *No information provided*
>>>
>>> *TAG review*
>>> *No information provided*
>>>
>>> *TAG review status*
>>> Not applicable
>>>
>>> *Risks*
>>>
>>>
>>> *Interoperability and Compatibility*
>>> Firefox has shipped the SVG2 behavior for years. Bug for WebKit:
>>> https://bugs.webkit.org/show_bug.cgi?id=249080
>>>
>>> *Gecko*: Shipped/Shipping (
>>> https://bugzilla.mozilla.org/show_bug.cgi?id=265894#c190) Shipped in
>>> Firefox 56
>>>
>>> *WebKit*: No signal (
>>> https://github.com/WebKit/standards-positions/issues/571)
>>>
>>> *Web developers*: Positive 44 votes on the crbug issue, and additional
>>> 5 votes on the :hover bug https://crbug.com/40663285
>>>
>>> *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 information provided*
>>>
>>>
>>> *Debuggability*
>>> *No information provided*
>>>
>>> *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>?*
>>> Yes
>>>
>>> https://wpt.fyi/svg/linking/reftests/use-descendant-combinator-003.html
>>> https://wpt.fyi/svg/struct/reftests/use-inheritance-001.svg
>>> https://wpt.fyi/svg/struct/reftests/use-inheritance-nth-child-of.svg
>>> https://wpt.fyi/svg/struct/reftests/use-inheritance-nth-last-child-of.svg
>>>
>>> https://wpt.fyi/svg/styling/use-element-attr-selector-transition.tentative.html
>>>
>>> https://wpt.fyi/svg/styling/use-element-id-selector-transition.tentative.html
>>>
>>> *Flag name on about://flags*
>>> #enable-experimental-web-platform-features
>>>
>>> *Finch feature name*
>>> Svg2Cascade
>>>
>>> *Rollout plan*
>>> Will ship enabled for all users
>>>
>>> *Requires code in //chrome?*
>>> False
>>>
>>> *Tracking bug*
>>> https://crbug.com/40550039
>>>
>>> *Estimated milestones*
>>> Shipping on desktop 144
>>> Shipping on Android 144
>>> Shipping on WebView 144
>>>
>>> *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).
>>> *No information provided*
>>>
>>> *Link to entry on the Chrome Platform Status*
>>> https://chromestatus.com/feature/5134266027606016?gate=6607474169872384
>>>
>>> This intent message was generated by Chrome Platform Status
>>> <https://chromestatus.com/>.
>>>
>>> --
>>> Rune Lillesveen
>>>
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>>> .
>>>
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>
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Rune Lillesveen
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