ABAP error exception concept within SAP

*Syntax for TRY .. ENDTRY construct
TRY.
    CALL METHOD o1->m1.
    PERFORM f1.
  CATCH cx_root.  "Handler for all exceptions
       " ABAP code(What to do when error occures)........
ENDTRY.
FORM f1 RAISING cx_my.
  TRY.
    IF ...... RAISE EXCEPTION TYPE cx_my2. ENDIF.
      CALL METHOD o1->m3.
  CATCH cx_my1 cx_my3 INTO ex.
    RAISE EXCEPTION TYPE cx_my4.
  CATCH cx_my4.
     "Handler for exceptions of type cx_my4
     " ABAP code(What to do when error occures)........
  CLEANUP.
     "Cleanup section, used to restore to a consistant state
     " ABAP code........
  ENDTRY.
ENDFORM.