Setting time zone commands

Hi!

Seeing no comments on the same issue I raised in
pgsql-general list, I am posting it here.
The documentation (Appendix B.2. Date/Time Key Words) says
that the following SQL's are legal, but actually they are
not:

SET TIME ZONE TO '<any time zone abbreviation>'
(examples:
SET TIMEZONE TO 'NZDT';
SET TIMEZONE TO 'EST';
)

However, the following SQL's are accepted by postgres:

SET TIME ZONE TO 0
SET TIME ZONE TO 9
SET TIME ZONE TO -4

Regards,
CN