import { InjectionToken } from '@angular/core';
import type { Observable } from 'rxjs';
/**
 * Injection token for an Observable that emits the visibility state of the document.
 *
 * This token provides an Observable that emits a boolean value indicating whether the document
 * is visible or hidden. It uses the `visibilitychange` event of the document to detect changes
 * in visibility state. The Observable is shared and replayed, ensuring that subscribers receive
 * the latest visibility state.
 */
export declare const PAGE_VISIBILITY: InjectionToken<Observable<boolean>>;