Module Pool - Event

Event Of Module Pool -

PAI & PBO is working as name states .
PBO ( Process Before Output ) - 

PAI  ( Process After Input   ) -

POH (Process on Help-Request)     - It gives F1 details .
   for calling -
       Process on Help-Request .
          Module f1_help_field2 Input .
example -
two functional module use for help  .
          Module f1_help_field2 Input .
                    call functional 'Help_object_show_for_field'
                            exporting
                                       doclangu            = sy-langu
                                        doctitle              = text-002
                                        called_for_tab   =  'demof1help'
                                        called_for_field = 'field1'     .

          endmodule .
                               or

         Module f1_help_field2 Input .

                    call functional 'Help_object_show'
                            exporting
                                        docclass            = 'TX'
                                       doclangu            = sy-langu
                                       docname            = 'demoforhelp'
                                        doctitle              = text-002
                           tables
                                        links                  = links

          endmodule .
          
POV ( Process on Value-Request ) - It gives F4 help  .
  for calling -
      Process on Value-Request .
       field f module Mod .
There are two functional Module
       DYNP_VALUES_READ
       DYNP_VALUES_UPDATE
that can read the values of screen fields and return values to them during POV event .