new and old as parameter in a function

Hi.

I'm having some trouble, and I would like to receive some input by the
pg community...

I would like to write a failry complex PLPGSQL trigger that calls a
secondary function. The trigger calls the function with the NEW record
that returns a variable of type RECORD whith the NEW variable modified
accordingly to a series of actions.

By Reading the documentation, I understand that I can write a PLPGSQL
function that receives a parameter of type RECORD, and returns a
parameter of type RECORD, and that this function is callable from a
Trigger.

But:

I haven't been able to write what's expressed above...

is there somebody that can provide some help and/or some examples?

thanks in advance,

=====
Riccardo G. Facchini