Here's an attempt from 2012. This approach doesn't work (the "trivial
plumbing" mentioned in the doc is actually highly non-trivial), but maybe
it will give some insights to find the right a proper solution:


On Fri, Jan 9, 2015 at 7:54 AM, Dimitri Glazkov <> wrote:

> For the record, I am a huge fan of exploring this. I tried a couple of
> times, but was unable to extract this primitive from Shadow DOM in a clean
> way. I talked with Tab late last year about restarting this effort, so this
> is timely.
> :DG<
> On Fri, Jan 9, 2015 at 7:49 AM, Anne van Kesteren <>
> wrote:
>> On Fri, Jan 9, 2015 at 4:35 PM, Brian Kardell <> wrote:
>> > For clarity, are you suggesting you'd control the matching boundary via
>> CSS
>> > somehow or you'd need an indicator in the tree?  A new
>> element/attribute or
>> > something like a "fragment root" (sort of a shadowroot-lite)?
>> I wasn't suggesting anything since I'm not sure what the best way
>> would be. It has to be some flag that eventually ends up on an element
>> so when you do selector matching you know what subtrees to ignore. If
>> you set that flag through a CSS property you'd get circular
>> dependencies, but perhaps that can be avoided somehow. Setting it
>> through an element or attribute would violate separation of style and
>> markup.
>> --

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