Live ORACLE

DECLARE
 past_due  EXCEPTION;
 acct_num  NUMBER;
BEGIN
 DECLARE ---------- sub-block begins
   past_due  EXCEPTION; -- this declaration prevails
   acct_num     NUMBER;
   due_date     DATE := SYSDATE
                          - 1;
   todays_date  DATE := SYSDATE;
 BEGIN
   IF due_date < todays_date THEN
     RAISE past_due; -- this is not handled
   END IF;
 END; ------------- sub-block ends

EXCEPTION
 WHEN past_due THEN -- does not handle raised exception

   dbms_output.Put_line('Handling PAST_DUE exception.');
 WHEN OTHERS THEN
   dbms_output.Put_line('Could not recognize PAST_DUE_EXCEPTION in this scope.');
END;
/  

Could not recognize PAST_DUE_EXCEPTION in this scope.

PL/SQL procedure successfully completed.

Scope of PL/SQL Exceptions