_internal_hosts()
 *
 * @since 6.2.0
 *
 * @param string $link The URL to test.
 * @return bool Returns true for internal URLs and false for all other URLs.
 */
function wp_is_internal_link( $link ) {
	$link = strtolower( $link );
	if ( in_array( wp_parse_url( $link, PHP_URL_SCHEME ), wp_allowed_protocols(), true ) ) {
		return in_array( wp_parse_url( $link, PHP_URL_HOST ), wp_internal_hosts(), true );
	}
	return false;
}