FOR integer loop bug?

Postgres 14.2

In commenting on a SO question I came across the below.

Given:

CREATE OR REPLACE FUNCTION public.for_loop_test()
RETURNS void
LANGUAGE plpgsql
AS $function$
BEGIN
FOR i IN 1..10 LOOP
RAISE NOTICE '%', i;
END LOOP;
END;

$function$
;

select for_loop_test();
NOTICE: 1
NOTICE: 2
NOTICE: 3
NOTICE: 4
NOTICE: 5
NOTICE: 6
NOTICE: 7
NOTICE: 8
NOTICE: 9
NOTICE: 10

Then, note 1...10:

CREATE OR REPLACE FUNCTION public.for_loop_test()
RETURNS void
LANGUAGE plpgsql
AS $function$
BEGIN
FOR i IN 1...10 LOOP
RAISE NOTICE '%', i;
END LOOP;
END;

$function$

select for_loop_test();
for_loop_test
---------------

If you do:

FOR i IN 1....10 LOOP

or

FOR i IN 1.10 LOOP

You get:

ERROR: syntax error at or near ".."
LINE 6: FOR i IN 1....10 LOOP

ERROR: syntax error at or near "1.10"
LINE 6: FOR i IN 1.10 LOOP

respectively.

Why is the three period form allowed through and why does it produce no
result?

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com