/**
 * Where a widget put its overlay, when it did not put it inside itself.
 *
 * A portalled popup is the one part legitimately outside its field's root, so it cannot be found by
 * containment. Two ways to look for it that do not work:
 *
 * - **By class, across the document.** Returns whichever field rendered first, so a page with two
 *   selects reports one of them twice and the other never.
 * - **By the id the opener names, and no further.** A trigger names the *listbox*; the popup that
 *   holds it is that element's ancestor. Scoping the search to the named element finds no popup,
 *   reports it absent, and then reads `aria-expanded="true"` beside a missing popup as an incoherent
 *   state — a violation reported against a widget that was behaving correctly.
 *
 * The right way is the relationship the widget itself declared, followed all the way out: take the
 * element the opener's `aria-controls` names, then walk up to the outermost ancestor that is still
 * outside the field. That is the portalled tree, and every part inside it belongs to this widget.
 */
/**
 * The portalled subtree belonging to `widgetRoot`, or `null` when the widget keeps its overlay
 * inside itself — which is equally conforming, and the reason this returns `null` rather than
 * throwing.
 */
export declare function portalRootFor(widgetRoot: Element): Element | null;