rest_validate_request_arg

 *
 * @see get_avatar_url()
 *
 * @param mixed $id_or_email The Gravatar to retrieve a URL for. Accepts a user_id, gravatar md5 hash,
 *                           user email, WP_User object, WP_Post object, or WP_Comment object.
 * @return array Avatar URLs keyed by size. Each value can be a URL string or boolean false.
 */
function rest_get_avatar_urls( $id_or_email ) {
	$avatar_sizes = rest_get_avatar_sizes();