Parameter NOT NULL to CREATE DOMAIN not the same as CHECK (VALUE IS NOT NULL)

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The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/sql-createdomain.html
Description:

The manual claims:

The syntax NOT NULL in this command is a PostgreSQL extension. (A
standard-conforming way to write the same would be CHECK (VALUE IS NOT
NULL). […])

But both variants differ when composite types are involved:

CREATE TYPE complex AS (real float8, imag float8);

CREATE DOMAIN d1 AS complex NOT NULL;
CREATE DOMAIN d2 AS complex CHECK (VALUE IS NOT NULL);

SELECT '(,)'::d1; -- allowed
SELECT '(,)'::d2; -- not allowed

Kind Regards,
Jan Behrens