/**
 * Checks whether the Safari's Privacy Preserving Ad Measurement setting is on.
 * The setting is on when the value is not undefined.
 * A.k.a. private click measurement, privacy-preserving ad attribution.
 *
 * Unfortunately, it doesn't work in mobile Safari.
 * Probably, it will start working in mobile Safari or stop working in desktop Safari later.
 * We've found no way to detect the setting state in mobile Safari. Help wanted.
 *
 * @see https://webkit.org/blog/11529/introducing-private-click-measurement-pcm/
 * @see https://developer.apple.com/videos/play/wwdc2021/10033
 */
export default function getPrivateClickMeasurement(): string | undefined;