Display LV cluster element value as an expression

I have a custom step type with a VI that has a cluster as input. I would like to display the value of a particular element of the cluster in the description of the step. I know how to get the value of other data-types with the expression

Step.TS.SData.ViCall.Parms["Parameter Name"].ArgVal

Since "Parameter Name" will be a cluster in my case, I can't find how to retrieve the value of a element.