`attachShadow` is called twice on the same element: first `{ mode: 'open' }`, then later `{ mode: 'open' }` again on a host that is NOT a custom element and was NOT given a declarative shadow root. What is the result of the second call?
const host = document.createElement('div');
host.attachShadow({ mode: 'open' });
host.attachShadow({ mode: 'open' }); // second call