code: func (f *WaitFilter) Add(obj types.ManagedObjectReference, kind string, ps []string, set ...types.BaseSelectionSpec) *WaitFilter {
  	spec := types.ObjectSpec{
  		Obj:       obj,
  		SelectSet: set,
  	}
  
  	pset := types.PropertySpec{
  		Type:    kind,
  		PathSet: ps,
  	}
  
  	if len(ps) == 0 {
  		pset.All = types.NewBool(true)
  	}
  
  	f.Spec.ObjectSet = append(f.Spec.ObjectSet, spec)
  
  	f.Spec.PropSet = append(f.Spec.PropSet, pset)
  
  	return f
  }
docs: // Add a new ObjectSpec and PropertySpec to the WaitFilter