These built in PDG variables are available everywhere:
@pdg_input - always evaluates to the first input of the current workitem. Use @pdg_input.1 and @pdg_input.2 etc. to address other inputs. When a workitem is being evaluated on the farm, this is how to make sure the network being evaluated has the correct inputs for that workitem. Do not use @pdg_output for this purpose, as the workitem has not computed yet and so has no output.
