Unclear how specificity of ::cue() and ::cue-region() should be calculated

[dd8]

Should the selectors passed as an argument be taken into consideration or ignored when calculating specificity?

::cue /* a=0 b=0 c=1 */
::cue(div) /* is this a=0 b=0 c=1  or a=0 b=0 c=2 */
::cue-region /* a=0 b=0 c=1 */
::cue-region(#first) /* is this a=0 b=0 c=1  or a=1 b=0 c=1 */

Looking at 'Calculating a selector’s specificity' in selectors-4 doesn't make things clear since pseudo classes that take selectors as parameters are special-cased:
https://drafts.csswg.org/selectors/#specificity-rules

[silviapfeiffer]

You'll want to check the WebVTT spec: it talks about applying the selectors: https://www.w3.org/TR/webvtt1/#the-cue-pseudo-element and https://www.w3.org/TR/webvtt1/#the-cue-region-pseudo-element

[dd8]

I can't see any definition for the specificity for ::cue(selector) and ::cue-region(selector) anywhere. The specificity is used when there are multiple rules that match and declare the same property value:
https://drafts.csswg.org/css-cascade/#cascade-sort

There are specificity rules for :is() :where() and other selectors that take a selector list as a parameter:
https://www.w3.org/TR/selectors/#specificity-rules

In example 2 the the specificity decides whether color:papayawhip or color:peachpuff is used for items matching video::cue(b):
https://www.w3.org/TR/webvtt1/#styling

• if the specificity of ::cue(<selector>) is zero like the :where(<selector>) (so A=0, B=0, C=0) then the color of items matching video::cue(b) is papayawhip (because :cue with no selector has higher specificity and wins the cascade)
• if the specificity of ::cue(<selector>) is the same as ::cue without a selector (so A=0,B=0, C=1) then the color of items matching video::cue(b) is peachpuff (because both selectors have the same specificity, so last in order of declaration wins)
• if the specificity of ::cue(<selector>) is calculated like :is(<selector>) (so A=0,B=0, C=1 in this example) then the color of items matching video::cue(b) is peachpuff (because both selectors have the same specificity, so last in order of declaration wins)

The difference between the last two becomes clearer if the universal selector is used:

   video::cue {
     background-image: linear-gradient(to bottom, dimgray, lightgray);
     color: papayawhip;
   }
   video::cue(*) {
     color: peachpuff;
   }

• if the specificity of ::cue(*) is the same as ::cue without a selector (so A=0,B=0, C=1) then the color of items matching video::cue(*) is peachpuff (because both selectors have the same specificity, so last in order of declaration wins)
• if the specificity of ::cue(*) is calculated like :is(*) (so A=0,B=0, C=0) then the color of items matching video::cue(*) is papayawhip (because :cue with no selector has higher specificity and wins the cascade)

Background: I'm adding support for ::cue() and ::cue-region() to an existing CSS engine. I need to know the specificity of these selectors to do this interoperably.

[dd8]

The specificity wording for :host() and :host-context() may be a good starting point:
https://drafts.csswg.org/css-scoping/#host-selector

[gkatsev]

I would need to spend more time on this, including investigating current implementations, but my current reading and knowledge of the spec seems like the intent was to have ::cue and ::cue() behave in a similar way to :host(). So, ::cue would have the specificity of a pseudo-element and ::cue() would have a specificity of a pseudo-element plus the specificity of the argument given.

You are correct that the spec doesn't currently make this explicit, and it would be something that should be updated in the spec.

[silviapfeiffer]

It wasn't added to the spec as the expectation was that the CSS specification provides for that kind of specificity, so they was no need to duplicate.

…

On Fri, Oct 29, 2021, 6:56 AM Gary Katsevman ***@***.***> wrote: I would need to spend more time on this, including investigating current implementations, but my current reading and knowledge of the spec seems like the intent was to have ::cue and ::cue() behave in a similar way to :host(). So, ::cue would have the specificity of a pseudo-element and ::cue() would have a specificity of a pseudo-element plus the specificity of the argument given. You are correct that the spec doesn't currently make this explicit, and it would be something that should be updated in the spec. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#499 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAXFQL4RPX3OUEXLFXUEGTUJGTILANCNFSM5GDT3BTQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.