/**
 * Tracks visibility of the page.
 *
 * @returns Visibility state of the [`document`](https://developer.mozilla.org/docs/Web/API/Document), which is `'visible'` by default.
 *
 * @example
 * function Component() {
 *   const documentVisibility = useDocumentVisibility();
 *   if (documentVisibility === 'hidden') {
 *     // Reduce resource utilization to aid background page performance
 *   }
 *   // ...
 * }
 */
export default function useDocumentVisibility(): VisibilityState;