/**
 * #3306 The <ngx-extended-pdf-viewer> an element belongs to. With several viewers on one page, ids
 * aren't unique, so components look up the viewer's elements in this root instead of the whole document.
 * Falls back to the document if the element isn't part of a viewer (yet).
 */
export declare function viewerRoot(element: Element | null | undefined): Document | Element;
/** #3306 `getElementById()` within a viewer root (see {@link viewerRoot}) */
export declare function getViewerElementById<T extends HTMLElement = HTMLElement>(root: Document | Element, id: string): T | null;