[css-cascade] Provide a syntax for re-using cascade layers across encapsulation context?

[mirisuzanne]

This was raised in #4984, related to the Cascade level 5 spec.

From the spec:

Note: Layer name matching does not cross the shadow DOM boundary,
so the ordering of layers in the light DOM has no impact
on the order of identically-named layers in the shadow DOM.

Are there use-cases where an author would want to…

• Reference or adjust global layer, from inside shadow-DOM?
• Reference or adjust an encapsulated shadow-DOM layer, from the global styles?

I don't currently know of any use-cases, but if they exists we probably need a special syntax for that.

[css-meeting-bot]

The CSS Working Group just discussed Providing a syntax for reusing syntax across cascade layers, and agreed to the following:

• RESOLVED: Close this issue for lack of use cases.

The full IRC log of that discussion

<myles> Topic: Providing a syntax for reusing syntax across cascade layers
<astearns> github: https://github.com//issues/5854
<myles> miriam: In order to avoid complex width shadow dom, we've spec'ed layer names in shadow dom encapsulation do not refer to the same named layers outside of shadow dom. Layer names dont' cross shadow dom boundary
<bkardell_> q+
<myles> miriam: Is there any case where it would be useful? I don't know the usecases here
<astearns> ack bkardell_
<emilio> q+
<myles> bkardell_: I don't have an example I can say, or a solution. But i dont' know if the current boundary needs something more. Wher eyou actually declarative adopt stylesheets. This should be part of that conversation
<florian> q+
<myles> astearns: Isn't the solution constructable stylesheets?
<myles> bkardell_: It's an element, yes. But you can't declaratively do that today.
<myles> bkardell_: You need those concepts first.
<TabAtkins> q+
<astearns> ack emilio
<myles> bkardell_: There's a big discussion here about how these things work. and participate cooperatively under mutual suspicion
<myles> emilio: I was going to ask how would this boundary crossing look like exactly? Right now in the shadow tree, the stylesheets apply to itself, and maybe host and slotted. but they are different cascade levels anyway. So i'm not sure how that would even work
<astearns> ack florian
<myles> florian: It would seem to me that from a shadow dom reopening a layer that has been opened outsdie of it to change it is probably a foot gun. not having the ability to do that sounds reasonable
<myles> florian: OTOH, the revert layer to a named layer, if we get that, doing that from inside the shadow dom does not sound crazy. if your components are all assuming the entire page will use bootstrap and your design system, and you're inside your shadow dom, and you want to revert layer to the design system layer, or revert ot bootstrap layer, it would be nice to call them. For now we dont' have this but it's not outlandish
<myles> emilio: But the stylesheets inside/outsdie the style root don't interact at all
<myles> astearns: We don't want to add interactions
<myles> TabAtkins: It's because you've imported those layer names as well
<astearns> ack TabAtkins
<myles> TabAtkins: AFAICT we don't need to do this b/c shadow dom separates styles arleady. You shouldn't get normal styles across anyway. Similar with host or part, those are applying styles in either the tree or the outer context, which is separate on a higher context already, so i don't think there's any place wehre the styles touch closely enough for layer context to matter. So this is nil.
<bkardell_> +1
<myles> fantasai: Let's close this, and if it's a problem later, someoen will file it again with a use case hopefullly
<myles> astearns: sound good?
<myles> florian: My previous comment made no sense given how things work
<myles> RESOLVED: Close this issue for lack of use cases.