An SAP Consultant: ABAP - Events in Dialog programming

Modulpool programs can have 4 events in the flow logic.

PROCESS BEFORE OUTPUT. (It is also called PBO).
This event is triggered before screen is displaye.
PROCESS AFTER INPUT. (It is also called PAI).
This event is triggered based on user action on screen.
PROCESS ON HELP-REQUEST.(It is also called POH).
It is triggered when u press F1 on screen for screen element .Calling Help Texts from Dialog Modules.

CALL FUNCTION 'HELP_OBJECT_SHOW_FOR_FIELD'
  EXPORTING
    DOKLANGU         = SY-LANGU
    DOKTITLE         = TEXT-002
    CALLED_FOR_TAB   = 'DEMOF1HELP'
    CALLED_FOR_FIELD = 'FIELD1'.

PROCESS ON VALUE-REQUEST.(It is also called POV).
It is triggered when we press F4 on screen for the screen element.
Use below FM to get f4 help for the field.

CALL FUNCTION 'F4IF_FIELD_VALUE_REQUEST'
  EXPORTING
    TABNAME     = 'DEMOF4HELP'
    FIELDNAME   = 'CARRIER1'
    DYNPPROG    = PROGNAME
    DYNPNR      = DYNNUM
    DYNPROFIELD = 'CARRIER'.