access to record's field in dynamic SQL doesn't work

Hi

I played with one dynamic access to record's fields. I was surprised so I
cannot to access to record field from dynamic SQL. Is there some reason why
it is not possible? Today all composite types in PL/pgSQL are records:

do $$
declare r record; _relname varchar;
begin
for r in select * from pg_class limit 3
loop
execute 'select ($1).relname' using r into _relname;
raise notice '%', _relname;
end loop;
end;
$$;
ERROR: could not identify column "relname" in record data type
LINE 1: select ($1).relname
^
QUERY: select ($1).relname
CONTEXT: PL/pgSQL function inline_code_block line 6 at EXECUTE

but:
do $$
declare r record; _relname varchar;
begin
for r in select * from pg_class limit 3
loop
--execute 'select ($1).relname' using r into _relname;
raise notice '%', r.relname;
end loop;
end;
$$;
NOTICE: pg_statistic
NOTICE: pg_type
NOTICE: pg_toast_1255

and

postgres=# do $$
declare r pg_class; _relname varchar;
begin
for r in select * from pg_class limit 3
loop
execute 'select ($1).relname' using r into _relname;
raise notice '%', _relname;
end loop;
end;
$$;
NOTICE: pg_statistic
NOTICE: pg_type
NOTICE: pg_toast_1255

it is working too.

Why there is difference between typed composite and record type although
internally should be same?

Regards

Pavel