Special RestrictonTarget.fromElement() behavior for elements associated with a shadowRoot?

[markafoltz]

Elements attached to a shadowRoot either are not rendered at all or are rendered in special circumstances (fullscreen, picture-in-picture). If a developer tries to restrict to an element attached to a shadowRoot, what should happen?

This may "just work" if the restriction conditions apply consistently to shadow DOM elements and the underlying implementation works as intended (i.e, it is able to capture a fullscreen element). But some investigation may be needed to confirm.