TIMEZONE names

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/13/datatype-datetime.html
Description:

The documentation states that some timezone names are recognized.  As far as
I understand others aren't.

This seems to be true:
$psql postgres -c "set TIMEZONE='bug' ; show timezone;"
ERROR:  invalid value for parameter "TimeZone": "bug"
$ echo $?
1

However adding a correct numerical offset leads Postgresql to accept a
non-existing timezone name:
$ psql postgres -c "set TIMEZONE='bug-1' ; show timezone;"
$ echo $?
0

Thank you.