After taking a closer look into the UMA, I realized that the use counter was not measuring active and intentional usage of these properties. Instead, it largely captures cases when an element’s resolved css values are retrieved (most commonly via `getComputedStyle()`, also via opening dev tools).
Because the default width values are non-zero (medium) and their corresponding style’s default is none, the counter can fire even when authors never explicitly set these or retrieve these properties. This happens because `getComputedStyle()` requests/serializes styles for all properties on the element, not just the one an author may care about. As a result, the ~2.37% figure can be treated as a very high upper bound on potential exposure rather than a granular measurement of these specific properties. Unfortunately, with the current setup it is not trivial to architect a use counter that measures only when developers meaningfully use these properties as opposed to incidental serialization during style queries. To get some directional signal, I manually surveyed the top 10 sites that the counter fired for and did not find any that were doing anything special with these properties. That said, each behavior change (for the computed and for the resolved) is guarded by its own finch feature flag, which provides a reliable rollout plan and kill switch if we observe unexpected impact on developers. On Wednesday, February 4, 2026 at 8:24:06 AM UTC-8 Daniel Bratell wrote: > LGTM2, with the plan outlined by Vlad. > > /Daniel > On 2026-02-04 17:16, Vladimir Levin wrote: > > I think the 2.37% use case is definitely interesting since if scrapers are > causing this, I would expect the number to either be much higher (scrapers > accessing this on most sites) or much lower (it's a negligible use case). > > That being said, I'm also not convinced that these are "real developers" > doing this on more than 2% of sites. > > Is it possible to check httparchive for a random sampling of websites that > trigger this UMA and see if there is a pattern that emerges or whether > there is script that accesses these properties? > > In either case, in light of both Firefox and Safari shipping and the fact > that outlines don't affect box geometry, I'm inclined to approve with a > note to be cautious in launching this and follow a finch rollout that > propagates the feature to the stable channel slowly. > > With that, LGTM1. > > Also, it would be nice to follow up about the 2.37% to see if there is a > solid explanation > > Thanks, > Vlad > > On Monday, February 2, 2026 at 3:05:48 PM UTC-5 Alex Russell wrote: > >> Why would scrapers opt into metrics reporting? Seems an unlikely >> explanation for elevated use. Do we have other views onto it, e.g. from >> Edge histograms? >> >> Best, >> >> Alex >> >> On Thursday, January 29, 2026 at 2:53:02 PM UTC-8 Sam Davis Omekara wrote: >> >>> Hi, >>> >>> Thanks for the questions. Find below my responses: >>> >>> >>> - Question: As a non-CSS expert, can you help me better understand >>> what "applying that special-case becomes ambiguous and difficult to >>> define >>> consistently"? Is this in terms of code that authors would write, or >>> prose >>> for spec authors? An example would be helpful here. >>> - Answer: The ambiguity is primarily around spec semantics. Gap >>> decorations extended the column-rule-* properties to accept value >>> lists and >>> `repeat()` patterns. The previous rule (“if style is none/hidden, >>> then >>> computed width is 0”) is straightforward for a single value, but with >>> lists >>> and repeats you no longer have a clean, well-defined way of >>> expressing this >>> behavior. For example, from the CSSWG discussion: >>> - column-rule-style: solid dashed none; >>> - column-rule-width: 1px 2px; >>> - This cycles to: “1px solid, 2px dashed, (1px) none, 2px solid, >>> 1px dashed, (2px) none …”. >>> - Setting the width to zero in this case depending on the style >>> at any point in the expansion isn’t well-defined. >>> - Also, `repeat()` syntax is preserved at computed-value time, >>> which further prevents expanding lists and applying a clean >>> index-based >>> rule: >>> - column-rule-style: repeat(2, solid none dashed); >>> - column-rule-width: 1px 2px; >>> - This would expand to: “1px (solid), 2px (none), 1px(dashed), >>> 2px(solid), 1px(none), 2px (dashed) …” But computed values explicitly >>> do >>> not perform this expansion, so any rule that depends on per-index >>> alignment >>> between style and width cannot be spec'd in a well-defined way. >>> - Question: 2.37% of page views is a lot of page views. Why do we >>> feel confident that border-width needs backwards compat considerations >>> for >>> getComputedStyle but column-rule-width and outline-width don't? Are you >>> saying that 2.37% of the use counters are coming from fingerprinting? >>> I'm >>> also not sure what it means for a scraper to trigger a UseCounter - can >>> you >>> clarify? I've typically thought of scraping as a server-side operation - >>> are these web extensions? >>> - Why do we feel confident that border-width needs backwards compat >>> considerations for getComputedStyle and column-rule-width and >>> outline-width >>> don’t? >>> - `border-*-width` properties are more commonly used and are >>> tied to the box model, so changing what getComputedStyle() returns >>> is more >>> likely to affect existing scripts that compute geometry or layout >>> related >>> behavior. In contrast, outline-width and column-rule-width are >>> less >>> commonly used and are only used for visual decoration so returning >>> the >>> author-specified width rather than 0px should not affect the >>> element’s >>> geometry, making user-visible regressions less likely. >>> - On the 2.37% >>> - The use counter added was scoped to trigger when the >>> resolved value gotten from getComputedStyle is called on an >>> element where >>> style is none/hidden but width is non-zero. While 2.37% is high we >>> believe >>> the traffic is dominated by: >>> - Fingerprinting/Telemetry scripts that typically iterate >>> over every CSS property to build a unique “fingerprint” of the >>> browser. >>> - Generic serializers that read all styles to copy/paste or >>> inspect elements >>> - The default for these properties is *-width: medium and >>> *-style: none. This is also a contributing factor to this high >>> percentage. >>> So even if a site doesn’t explicitly set these values and is being >>> scraped, >>> by virtue of the defaults, the counter will get hit. >>> - On scrapers being server side >>> - In recent times, we’ve seen scrapers be headless browser >>> automation like Puppeteer or Selenium or client-side scripts in >>> real >>> browsers. They can execute Javascript and call getComputedStyle >>> which in >>> this case would expect the counter to be hit. >>> These tools often query hundreds of properties which >>> signals that a high query rate does not necessarily imply >>> meaningful >>> web-facing dependence on the current behavior. >>> - Also, we are not first movers in this case, Webkit and Gecko >>> have shipped this. >>> - + [email protected] for more details on this. >>> >>> >>> >>> On Thursday, January 22, 2026 at 6:21:07 PM UTC-8 Mike Taylor wrote: >>> >>>> On 1/21/26 1:46 p.m., Chromestatus wrote: >>>> >>> *Contact emails* >>>> [email protected], [email protected] >>>> >>>> >>>> >>>> *Explainer* >>>> *No information provided* >>>> >>>> *Specification* >>>> https://github.com/w3c/csswg-drafts/pull/11913/files >>>> >>>> *Summary* >>>> This proposal untangles ‘border-width’, ‘outline-width’, and >>>> ‘column-rule-width’ from their corresponding ‘*-style’ properties. >>>> Previously, if a ‘*-style’ property, such as ‘border-style’, was set to >>>> ‘none’ or ‘hidden’, the computed ‘*-width’, such as ‘border-width’, would >>>> resolve to ‘0px’, even if the width was explicitly set to ‘10px’. >>>> Following >>>> a resolution in the CSSWG [1], the computed values of ‘border-width’, >>>> ‘outline-width’, and ‘column-rule-width’ will now reflect their specified >>>> values, regardless of the associated style property's value. Similarly, >>>> the >>>> resolved values of ‘outline-width’, and ‘column-rule-width’ will now >>>> reflect their specified values, regardless of the associated style >>>> property's value. [1]: >>>> https://github.com/w3c/csswg-drafts/issues/11494#issuecomment-2675800489 >>>> >>>> *Blink component* >>>> Blink>CSS >>>> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ECSS%22> >>>> >>>> *Web Feature ID* >>>> *No information provided* >>>> >>>> *Motivation* >>>> Today, CSS special-cases ‘border-*-width’, ‘outline-width’, and >>>> ‘column-rule-width’ so that their computed value becomes ‘0px’ when the >>>> corresponding ‘*-style’ is ‘none’ or ‘hidden’, even if the author >>>> specified >>>> a nonzero width. With Gap Decorations extending ‘column-rule-*’ properties >>>> to support lists/repeaters, applying that special-case becomes ambiguous >>>> and difficult to define consistently. Having ‘*-width’ values independent >>>> of ‘*-style’, provides an intuitive model for these properties and better >>>> reflects the author-specified value. >>>> >>>> As a non-CSS expert, can you help me better understand what "applying >>>> that special-case becomes ambiguous and difficult to define consistently"? >>>> Is this in terms of code that authors would write, or prose for spec >>>> authors? An example would be helpful here. >>>> >>>> >>>> *Initial public proposal* >>>> https://github.com/w3c/csswg-drafts/issues/11494 >>>> >>>> *Search tags* >>>> column-rule-width <http:///features#tags:column-rule-width>, >>>> border-width <http:///features#tags:border-width>, outline-width >>>> <http:///features#tags:outline-width> >>>> >>>> *TAG review* >>>> *No information provided* >>>> >>>> *TAG review status* >>>> Not applicable >>>> >>>> *Risks* >>>> >>>> >>>> *Interoperability and Compatibility* >>>> The interoperability risk is low as both Gecko and Webkit have already >>>> implemented these changes. Compatibility risk is also low. The resolved >>>> value for `border-width` via `getComputedStyle()` will remain 0px when >>>> `border-style` is set to `none`/ `hidden`, maintaining backward >>>> compatibility. For `outline-width` and `column-rule-width`, both computed >>>> and resolved values will show the specified values, as these properties >>>> are >>>> rarely queried and unlikely to impact existing content. To support the >>>> claim, we collected UseCounter data measuring how often these values are >>>> queried. The computed‑value counters for these properties are extremely >>>> low >>>> (<0.0001%). The resolved‑value counters for ‘column-rule-width’ and >>>> ‘outline-width’ show ~2.37% usage, which reflects calls to >>>> ‘getComputedStyle()’ rather than observable rendering usage. Since >>>> ‘getComputedStyle()’ is frequently queried by automated tooling (e.g. >>>> scrapers and fingerprinting scripts) that do not depend on property >>>> semantics, this usage does not indicate meaningful web‑facing reliance. As >>>> a result, the compatibility risk remains low. >>>> >>>> 2.37% of page views is a lot of page views. Why do we feel confident >>>> that border-width needs backwards compat considerations for >>>> getComputedStyle but column-rule-width and outline-width don't? Are you >>>> saying that 2.37% of the use counters are coming from fingerprinting? I'm >>>> also not sure what it means for a scraper to trigger a UseCounter - can >>>> you >>>> clarify? I've typically thought of scraping as a server-side operation - >>>> are these web extensions? >>>> >>>> thanks! >>>> >>>> >>>> *Gecko*: Shipped/Shipping ( >>>> https://bugzilla.mozilla.org/show_bug.cgi?id=1998285) >>>> >>>> *WebKit*: Shipped/Shipping ( >>>> https://bugs.webkit.org/show_bug.cgi?id=304940) >>>> >>>> *Web developers*: No signals >>>> >>>> *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 extra functionality is needed in Devtools to debug this feature >>>> update. >>>> >>>> *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/results/css/css-backgrounds/animations/border-width-interpolation.html >>>> >>>> https://wpt.fyi/results/css/CSS2/ui/outline-width-096.xht >>>> https://wpt.fyi/results/css/CSS2/borders/border-width-011.xht >>>> https://wpt.fyi/results/css/CSS2/borders/border-width-012.xht >>>> https://wpt.fyi/results/css/css-ui/parsing/outline-width-computed.html >>>> https://wpt.fyi/results/css/css-ui/outline-009.html >>>> https://wpt.fyi/results/css/css-ui/animation/outline-width-interpolation.html >>>> >>>> https://wpt.fyi/results/css/css-multicol/parsing/column-rule-width-computed.html >>>> >>>> https://wpt.fyi/results/css/css-multicol/parsing/column-rule-computed.html >>>> https://wpt.fyi/results/css/css-backgrounds/animations/border-width-interpolation.html >>>> >>>> *Flag name on about://flags* >>>> *No information provided* >>>> >>>> *Finch feature name* >>>> DecoupleComputedBorderWidthFromStyle,DecoupleResolvedColumnRuleWidthFromStyleEnabled >>>> >>>> >>>> >>>> *Rollout plan* >>>> Will ship enabled for all users >>>> >>>> *Requires code in //chrome?* >>>> False >>>> >>>> *Tracking bug* >>>> https://issues.chromium.org/issues/393631108 >>>> >>>> *Estimated milestones* >>>> Shipping on desktop 146 >>>> Shipping on Android 146 >>>> Shipping on WebView 146 >>>> >>>> *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/5133099851317248?gate=5201902006173696 >>>> >>>> This intent message was generated by Chrome Platform Status >>>> <https://chromestatus.com>. >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "blink-dev" group. >>>> >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> >>>> >>>> To view this discussion visit >>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/69711ef3.710a0220.3080c5.02c3.GAE%40google.com >>>> >>>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/69711ef3.710a0220.3080c5.02c3.GAE%40google.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > To view this discussion visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/cbe45224-f32d-41aa-851a-a050c272fc84n%40chromium.org > > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/cbe45224-f32d-41aa-851a-a050c272fc84n%40chromium.org?utm_medium=email&utm_source=footer> > . > > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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