Precedence of a TRIGGER vs. a CHECK on a column

Hi,

I've got a table:

<code language="SQL">
CREATE TABLE "common"."dynamic_enum"
(
"pk_id" integer DEFAULT
nextval('"common"."pw_seq"')
, "enum_type" common.non_empty_name
, "value" integer NOT NULL DEFAULT
nextval('"common"."de_local_seq"')
, "name" common.not_all_digits
, "display_name" varchar(256)
, "description" varchar(4000)
, "sort_order" common.sort_order_type
, "is_internal" boolean NOT NULL DEFAULT false
, LIKE "common"."usage_tracking_columns" INCLUDING DEFAULTS
)
WITHOUT OIDS
;
</code>

Where common.non_empty_name is defined as:

<code language="SQL">
CREATE DOMAIN common.non_empty_name AS varchar(256) NOT NULL
CONSTRAINT Not_Empty CHECK ( VALUE<>'' );
</code>

I'm using COPY to load some data and I want to set the "enum_type" which is
not present in the file which contains the to-be-loaded data. So, I define
a trigger:

<code language="PL/pgSQL">
CREATE OR REPLACE FUNCTION "merchandise".trg_insert_de_temp()
RETURNS trigger AS '
BEGIN
IF ( NEW."enum_type" IS NULL) THEN
NEW."enum_type" =''group_code'';
END IF;
RETURN NEW;
END;
' LANGUAGE plpgsql VOLATILE;
</code>
<code language="SQL">
CREATE TRIGGER zz_set_enum_type_temp BEFORE INSERT ON
"common"."dynamic_enum"
FOR EACH ROW EXECUTE PROCEDURE "merchandise".trg_insert_de_temp();

</code>

But, when I do the COPY I get:

<snip type="psql-output">
psql:load_yurman_merchandise.de.sql:59: ERROR: domain non_empty_name does
not allow null values
CONTEXT: COPY dynamic_enum, line 1: "BRACELET Bracelet"
</snip>

So it seems that the CHECK definied for the non_empty_name domain is being
applied before the trigger is executed. Yet, it seems that NON NULL
constraints are applied after triggers get called.

Questions:
1. Is the just-described ordering accurate?
2. Is that intended (e.g., the way it "should" be because of, say, SQL
standard)
3. Is there a work-around (short of changing the definition for the
relevant column)?

Thanks,

== Ezra Epstein