escape_string_warning doesn't work

Hello

I tried the option escape_string_warning, but why it doesn't get a warning
with the following code:

SET escape_string_warning TO on;
CREATE DOMAIN email AS character varying(50) CHECK (((VALUE)::text ~
'^[a-z0-9]+([_\\.-][a-z0-9]+)*@([a-z0-9]+([.-][a-z0-9]+)*)+\\.[a-z]{2,}$'::t
ext));

regards,

Tjibbe