in src/focus-zone.ts [357:376]
function updateFocusedElement(to?: HTMLElement, directlyActivated = false) {
const from = currentFocusedElement
currentFocusedElement = to
if (activeDescendantControl) {
if (to && isActiveDescendantInputFocused()) {
setActiveDescendant(from, to, directlyActivated)
} else {
clearActiveDescendant()
}
return
}
if (from && from !== to && savedTabIndex.has(from)) {
from.setAttribute('tabindex', '-1')
}
to?.setAttribute('tabindex', '0')
}