AIST0002-User Exit - Validation of user defined field

Question

I have implemented the enhancement aist0002.  I added a user defined field in a user defined subcreen and added it to the leasing tabstrip.  I would like to validate this field against a another field in sap's leasing subscreen.  In the pai of the user defined subsrceen the field of the other subscreen does not get filled.  Is there a way to access the field of the other subscreen on the leasing tabstrip from the pai module of the user defined subscreen?
Thank you
Tom

Answer 1

Thank you for your response but I am not sure where the import occurs?
This is the pai of the user subscreen 9000 for AS01.
form edit_input .
  data: itab type lfza.
  if anlu-zzempfk is not initial.
    select * from lfza into itab
            where empfk = anlu-zzempfk and
                  lifnr = anla-leafi.
    endselect.
    if sy-subrc <> 0.
      set cursor field 'ANLU-ZZEMPFK'.
      message e007(zvalid).
    endif.
  endif.
endform.                
Function exit EXIT_SAPLAIST_002 include zxaisu03   
looks like this:
anlu = i_anlu.
anla = i_anla.
Data gets moved to anlu or anla if it was already built.  They are empty when it is a create transaction(as01).
Function exit exit_saplaist_003. include zxaisu04
looks like this:
  e_anlu = anlu.
After the subscreen is processed it exports the data to global variable.
The problem is the pai module for the user subscreen 9000, the  field anla-leafi is not filled.  This field is  located in sap's subsceen 1403.  It has data in the screen field.  My assumption is that it would be accessible as global data that could be used by my user defined subscreen once I began the validation in the pai of subscreen 9000.
Could you provide more insight on how I would access the field from the other subscreen?