zone), `english' (readable English), `lapsed' (elapsed time),
`combined-lapsed' (both the original date and the elapsed time),
`original' (the original date header), `iso8601' (ISO8601
zone), `english' (readable English), `lapsed' (elapsed time),
`combined-lapsed' (both the original date and the elapsed time),
`original' (the original date header), `iso8601' (ISO8601