SQL & PL/SQL

CREATE OR REPLACE TRIGGER TRIG_EMP
AFTER UPDATE
ON EMP
FOR EACH ROW

DECLARE

CNT NUMBER := 0 ;

BEGIN

UPDATE EMP_bkp
SET COMM=999
WHERE ENAME ='SMITH';

COMMIT; -- it will generate error as commit cnt b use inside trigger so code wil go to exception blk.

exception
when others then
declare
PRAGMA AUTONOMOUS_TRANSACTION;
begin
commit;
end;
END;


why code is giving error?cant i put PRAGMA AUTONOMOUS_TRANSACTION in exception block although i have putted it into declare.. begin.. end block.
It might be unnecesary question but i m in delema why we cnt use pragma in exception block when any error ocur in code.as we can call any proc,func via exception block then why not we can call pragma?