Order of "WITH RECURSIVE" output

Hi all.
Take this example from src/test/regress/sql/with.sql:

WITH RECURSIVE subdepartment(level, id, parent_department, name) AS
(-- non recursive termSELECT 1, * FROM department WHERE name = 'A'
UNION ALL
-- recursive termSELECT sd.level + 1, d.* FROM department AS d, subdepartment AS sd    WHERE d.parent_department =
sd.id
)
SELECT * FROM subdepartment ORDER BY name;
level | id | parent_department | name
-------+----+-------------------+------    1 |  1 |                 0 | A    2 |  2 |                 1 | B    3 |  3 |
               2 | C    3 |  4 |                 2 | D    4 |  6 |                 4 | F 
(5 rows)

If I omit "ORDER BY", is the output *guaranteed* (according to some standard) to be ordered in "hierarchy"-order,
meaningeach parent-department is always output before its respective child, or do I have to calculate a "level" column
(likein the example above) and specify "ORDER BY LEVEL" to be 100%? 

I'm using WITH RECURSIVE as sub-queries to build up arrays of parents in each output-row and would like as little
overheadas possible and hence avoid unnecessary sorting. 

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / CTO
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