This was mistakenly applied to NEWS.27 on the master branch in
2021-05-09 "; Fix decoded-time-set-defaults typo in NEWS.27."
but that has now been reverted (bug#48298).
(that computes the date of an ordinal day), 'decoded-time-add' (for
doing computations on a decoded time structure), 'make-decoded-time'
(for making a decoded time structure with only the given keywords
-filled out), and 'encoded-time-set-defaults' (which fills in nil
+filled out), and 'decoded-time-set-defaults' (which fills in nil
elements as if it's midnight January 1st, 1970) have been added.
*** In the DST slot, 'encode-time' and 'parse-time-string' now return -1