In Bug 77503, an element becomes able to have multiple shadow root.
Next step is to ensure they are rendered correctly.
We should confirm:
(1) The youngest shadow root is rendered correctly.
(2) <content> element is rendered correctly.
Currently we don't have <shadow> element. Supporting <shadow> element will be another step.
The description is not clear. We have fuzzers. We've written many tests.
Let's reopen when we get some clearer idea about this.