Exception Propaqation

Unhandled exceptions are passed to the system containing the PL/SQL engine.
Exceptions can be re-raised in their handler; passes control to handler in outer block.
Exceptions can be ignored by using NULL as the handler.
Generic exception handler implemented by:
   WHEN Exception1 THEN Statements1;
   WHEN Exception2 THEN Statements2;
   ...
   WHEN OTHERS THEN Statementsn;
   END;