TNAPR vs NAST table??

TNAPR vs NAST tables in o/p type configuration (NACE) -

>(say , in terms of SAP script )

what both of this table actually does ---pls specify.. ???

o/p type is a combination of 3 things:

1. Driver program

2. Subroutine pool

3. Script name / Form name(layout )

i have seen in case of MEDRUCK(Standard purchase order form) if u go to transaction code NACE then see the output type u will see a subroutine pool name (in IDES version of SAP ) ...but from se38 there will be no object of that name ..?

so for what purpose it is given there ?

and if i made changes the standard form MEDRUCK into my own form say ZMEDRUCK & add something through the subroutine pool ...am i required to enter the new subroutinepool name in o/p tyoe configaration or it will work fine ?

as im calling that subroutine (pool) from my ZMEDRUCK ....

plsss answer ...

thnks ,

SARIT