Do AGGREGATES consistently use sort order?

I have the following query:

select array_accum(name) from (select name from placenames where
desig='crater' order by name desc) a;

with array_accum defined as:

CREATE AGGREGATE array_accum (
   BASETYPE = anyelement,
   SFUNC = array_append,
   STYPE = anyarray,
   INITCOND = '{}'
);

Can I count on this aggregate to take each new item in sorted order
when it adds it to the state vector?  So that if I have the following:

oregon_2007_08_20=# select * from (select name from placenames where
desig='crater' order by name desc) a;

 name
--------------------
 Yapoah Crater
 West Crater
 Twin Craters
 Timber Crater
 Red Crater
 Newberry Crater
 Nash Crater
 Mount Mazama
 Millican Crater
 Little Nash Crater
 Le Conte Crater
 Jordan Craters
 Diamond Craters
 Coffeepot Crater
 Cayuse Crater
 Black Crater
 Big Hole
 Belknap Crater
(18 rows)

I can always count on (note the order name):

\a
oregon_2007_08_20=# select array_accum(name) from (select name from
placenames where desig='crater' order by name desc) a;
array_accum
{"Yapoah Crater","West Crater","Twin Craters","Timber Crater","Red
Crater","Newberry Crater","Nash Crater","Mount Mazama","Millican
Crater","Little Nash Crater","Le Conte Crater","Jordan
Craters","Diamond Craters","Coffeepot Crater","Cayuse Crater","Black
Crater","Big Hole","Belknap Crater"}
(1 row)

I am interested in stitching a line out of points in postgis, but the
order/aggregate thing is a general question.

Thx
W