Re: [csswg-drafts] [css-position] Ability to set a positioned element's containing block to another element (#5952)

@dholbert 

> One possible constraint / concern here: the "search" here might need to be blocked from crossing boundaries of elements that form containing blocks for their fixed-position descendants (e.g. an element with `filter` or `transform` set to a non-default value).

Do they need to be blocked when going up (i.e. the positioned element is a descendant of an element that forms a containing block for their fixed-position descendant) or also going down, i.e. when the positioned element is outside that subtree, but wants to be positioned relative to an element within that subtree? 

Although, I seem to recall `<dialog>`'s positioning was an exception to this anyway.

> Similarly, it's worth thinking about how this would interact with / traverse `overflow:[hidden|scroll|auto]` and `contain:paint`.

Yup, #5699 is about exactly that.
While these would definitely be used together frequently, I think they are ultimately orthogonal issues. 

> (Though... is the intent here that the actual box-tree parenting of the positioned thing would be changed? i.e. does it just entirely "escape" any filters, transforms, `overflow` clipping, etc. that one of its nearby ancestors might otherwise impose on it? If so: then that would somewhat clarify how this would work in my previous comment. Though I suspect that reparenting would introduce other complications that I haven't thought through yet.)

Ideally, yes. Whether it *needs* to or we can still cover enough use cases without this is yet unknown.

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Received on Thursday, 11 February 2021 14:44:12 UTC