(1)This section applies for the purposes of sections 839 to 841.
(2)For the purposes of this section the relevant year, in relation to a payment, is the year which begins with the date it is made.
(3)If a payment is made for a period all of which is after the relevant year, it must be treated as made for the relevant year.
(4)If a payment is made for a period part of which is after the relevant year, it must be treated as if a corresponding part of it was made for the relevant year (and no part for a later period).