My question about autonomous transaction

Hello:

I have found the following wiki about autonomous transaction:

https://wiki.postgresql.org/wiki/Autonomous_subtransactions

But when I test it, I found the following error:

pgsql=# BEGIN;

BEGIN

pgsql=# INSERT INTO tab01 VALUES (1);

INSERT 0 1

pgsql=# BEGIN SUBTRANSACTION;

ERROR: syntax error at or near "SUBTRANSACTION"

LINE 1: BEGIN SUBTRANSACTION;

^

pgsql=#

So that sub transaction is still not supported in PostgreSQL,

Is my understanding right?

Best Regards