Trigger documentation problem

Hi all,

There's a problem with the documentation for triggers.
In the CREATE TRIGGER documentation page, the synopsis says:

CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
ON table FOR EACH { ROW | STATEMENT }
EXECUTE PROCEDURE func ( arguments )

and one of the examples given is:

CREATE TRIGGER if_dist_exists
BEFORE INSERT OR UPDATE ON films FOR EACH ROW
EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');

However, in the section 21.1 TRIGGER CREATION, one can read:

The trigger function must be created before the trigger is created as a
function taking no arguments and returning opaque.

Also, in the section 24.3 TRIGGER PROCEDURES:

They are created with the usual CREATE FUNCTION command as a function
with no arguments and a return type of OPAQUE.

Regards,

Antonio Sergio