[webcomponents] Difference between composed document and document flat tree (#382)

It's not clear to me there is a difference.

Also, does Shadow DOM work without there being a document? There is a lot of terminology around there not being a document at the root. Is that to account for shadow trees in something created through `document.createElement()` but never inserted? Will event dispatch there go through the shadow tree and such?

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/382