LGTM3 - Risk seems manageable even though it's unfortunately hard to
measure. That it has worked for such a long time in Gecko without major
push towards something else is a good sign. Good luck. We're all
counting on you.
/Daniel
On 2025-11-12 10:32, Mike Taylor wrote:
On 11/10/25 7:22 p.m., Rune Lillesveen wrote:
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?
That, or some display:none rule that didn't work before, starts
working now, which could be a major or minor issue.
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.
I spent some time poking through the Firefox bug and its various
associated bugs. I think it's a pretty good sign that this landed 8
years ago and the reported regressions were due to implementation bugs
that were quickly fixed.
The absence of bugs in Bugzilla isn't a perfect compat signal, but
it's at least promising.
In order to use-count this, we would have to run both ways of
cascading (or at least selector matching) to detect such cases.
This sounds like a lot of complexity (but feel free to respond telling
me it's trivial to implement). So, LGTM2 and hopefully I'm not wrong
about the risk here.
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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