can you tell me how to use rollback work in 'pgsql' function? and give me a exsample?

i see you wrote on this page 
http://archives.postgresql.org/pgsql-general/2005-07/msg00319.php
  
test exsample:
    create or replace function test()
    returns void as 
    '
    begin 
        delete from regiondata;
        rollback;
    end;
    'language 'plpgsql';
but exception a error:    CONTEXT:  PL/pgSQL function "test" line 3 at SQL statement 
Use others' words :
>It is important not to confuse the use of BEGIN/END for grouping statements
> in PL/pgSQL with the database commands for transaction control. PL/pgSQL's
> BEGIN/END are only for grouping; they do not start or end a transaction
and can you tell me how to use rollback work in 'pgsql' function?  and give me a exsample?

　　　　　　　　
 

　　　　　　　　alan.nee
　　　　　　　　neemem@gmail.com
　　　　　　　　　　2005-07-13