WHATWG
2026-03-16
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02:50
<sideshowbarker>
Nice surprise to see Lachlan Hunt commenting on an issue https://github.com/whatwg/html/issues/2177#issuecomment-4064231573
02:50
<sideshowbarker>
It’s been a long time since I can remember seeing him show up.
06:01
<annevk>
Yeah, I liked that too. I think he did it at least once before in the last couple of years, but I don't remember where.
14:31
<keithamus>
shadowrootslotassignment seems conspicuously absent from our shadowroot* template properties. Should we add it?
14:33
<keithamus>

dictionary ShadowRootInit {
  required ShadowRootMode mode;
  boolean delegatesFocus = false;
  SlotAssignmentMode slotAssignment = "named";
  boolean clonable = false;
  boolean serializable = false;
  CustomElementRegistry? customElementRegistry;
};

All of these have a shadowroot* attribute equivalent but slotassignment

14:33
<annevk>
keithamus: if it can be used as an attribute, prolly; I forgot how it works
14:34
<keithamus>
Sounds like enough to dig into it some more then
14:34
<annevk>
keithamus: is there an attribute for declarative shadow trees though? I'm not entirely sure how that would even work.
14:34
<annevk>
At least I thought slot assignment was purely imperative, but maybe something changed over the years.
14:35
<keithamus>
Slot assignment is imperative if the mode is manual, otherwise it’s based on name.
14:36
<keithamus>
So the attribute could just map to idl; allowing <template shadowrootalotassignment=manual>
14:38
<keithamus>
Right now if you want manual slot assignment you cannot use declarative shadow roots.
15:15
<annevk>
keithamus: if it works out fine it seems reasonable to add. Might be worth doing some blame as to why it wasn't added in the first place.
15:35
<keithamus>
https://github.com/mfreed7/declarative-shadow-dom/blob/master/README.md mfreed's explainer has notes on shadowroothost, shadowrootdelegatesfocus, but not slot assignment. I can't see any motivation for why this was avoided.
16:21
<keithamus>
annevk: https://github.com/whatwg/html/pull/12267 spec seemed easy enough. I've agenda+ and we can perhaps resolve that this should be a thing.
16:48
<annevk>
keithamus: it might have been fallout from those two things happening at a similar time but slot assignment ultimately winning and then declarative shadow roots not getting rebased properly
16:53
<keithamus>
Yeah you're probably right. https://github.com/whatwg/html/pull/6561, https://github.com/whatwg/html/pull/5465 are the two PRs, DSD got created before imperative slots, but merged after it (much later).
16:55
<jgraham>
OK, so in WebDriver BiDi we have a bunch of cases where we want to call into spec algorithms from a WebDriver endpoint, but where the algorithms have been written on the assumption that there's being called from WebIDL, as part of js execution (for example for video screen capture, or anything involving streams). Is there a better option here than defining a environment settings object and associated realm for running spec-internal script, and calling prepare to run a script to put that realm onto the JS stack before running anything? Conceptually it's a bit like running things in the Firefox parent process (but ofc not all browsers have that architecture; the idea is that it would be unobservable and it's just a spec hack to avoid everyone having to write their algorithms in a fully abstract way, but if there are unavoidable leaks that would be good to know)
17:05
<mfreed>
Re: the above questions about slot assignment, I think it was mostly manual slot assignment not being quite "done" by the time I put together the declarative shadow dom explainer. Thanks keithamus for finishing the job!
17:05
<mfreed>
Hi all, just a friendly reminder to post any discussion topics for this Thursday's joint CSSWG/WHATWG/OpenUI task force meeting to the meeting agenda issue: https://github.com/whatwg/html/issues/12240
17:23
<annevk>
I see Luke Warlow took care of the carry-over. Hopefully we start with that.