[whatwg/dom] Extension only API to query across shadow trees (Issue #1321)

### What problem are you trying to solve?

Certain browser extensions need to query elements across shadow trees in order to implement features such as autofill.

### What solutions exist today?

Chrome exposes `chrome.dom.openOrClosedShadowRoot`. Firefox exposes `element.openOrClosedShadowRoot`. Safari has `collectMatchingElementsInFlatTree` defined in window for Safari's autofill implementation.

### How would you solve it?

Ideally, we'd come up with an interoperable API for browser extensions that work across browsers.

### Anything else?

_No response_

-- 
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/1321
You are receiving this because you are subscribed to this thread.

Message ID: <whatwg/dom/issues/1321@github.com>