code: func (r *REST) Delete(ctx context.Context, name string, options *metav1.DeleteOptions) (runtime.Object, bool, error) {
  	for _, spc := range scheduling.SystemPriorityClasses() {
  		if name == spc.Name {
  			return nil, false, apierrors.NewForbidden(scheduling.Resource("priorityclasses"), spc.Name, errors.New("this is a system priority class and cannot be deleted"))
  		}
  	}
  
  	return r.Store.Delete(ctx, name, options)
  }
docs: // Delete ensures that system priority classes are not deleted.