in src/focus-zone.ts [404:413]
function clearActiveDescendant(previouslyActiveElement = currentFocusedElement) {
if (focusInStrategy === 'first') {
currentFocusedElement = undefined
}
activeDescendantControl?.removeAttribute('aria-activedescendant')
container.removeAttribute(hasActiveDescendantAttribute)
previouslyActiveElement?.removeAttribute(isActiveDescendantAttribute)
activeDescendantCallback?.(undefined, previouslyActiveElement, false)
}