Syntax for device check violation file assert statement

Hello,

I would like to ask how to write device check violation files (for example devcheck.scs) I can include in my model files and use to check for violations.

I believe the correct syntax for example for a vgs voltage check would be:

nmos_name assert mod=nmos_model_name expr="v(g)-v(s)" max =[max_voltage] duration=[duration of violation]

Let's say I want to modify the above assert statement so it checks only when another condition is true: I want to check vgs voltage only when vgd>0 for example

or when ids >0.  How would I write that?

Thank you!