form using plug-in file and "validation if"; how to?

Hello all,
I have a form that has multiple fields.
Some fields should change while filling the form based on specific field content.
I solve this using a static plug-in and the WA framework.
So, basically, some form fields are on the master form and other fields are in the static plug-in file.
But how can I handle errors?
I use the WA Server validation on the master page that contains the main form.
But how to hanle Server validation for the fields contained in the static plug-in?
I display validations errors using "validation sow if" SB.
But where should I put the errors and the various "validation show if" for the static plug-in fields?
TIA
tony