default partitions can be partitioned and have default partitions?

postgres=# CREATE TABLE t(i int)PARTITION BY RANGE(i);
CREATE TABLE
postgres=# CREATE TABLE t0 PARTITION OF t DEFAULT PARTITION BY RANGE(i);
CREATE TABLE
postgres=# CREATE TABLE t00 PARTITION OF t0 DEFAULT; -- oh yes
CREATE TABLE
...

Not sure how it could be useful to partition default into subpartitions of
lists, ranges, hashes.

Justin