[performance] applying the polyfill in self contained web components with light dom about focus-visible HOT 1 OPEN

You could argue of course that it's the responsibility of the parent shadow root to apply the polyfill, but that would not be an easy and straigthforward migration path for our consumers (not as easy as importing a polyfill); it's easily forgotten.

Alternatively, you could recursively apply applyFocusVisiblePolyfill to all shadowRoots found from the document. I don't know what the performance implication would be, but you probably run again into the risk of handling the same root multiple times in case you encounter components already applying this?
Also, you would need to keep track of newly created shadowRoots, so that would probably be undoable (or just way too costly...)

from focus-visible.