code: func EnvValueRetriever(pod *corev1.Pod) EnvVarResolverFunc {
  	return func(e corev1.EnvVar) string {
  		gv, err := schema.ParseGroupVersion(e.ValueFrom.FieldRef.APIVersion)
  		if err != nil {
  			return ""
  		}
  		gvk := gv.WithKind("Pod")
  		internalFieldPath, _, err := scheme.Scheme.ConvertFieldLabel(gvk, e.ValueFrom.FieldRef.FieldPath, "")
  		if err != nil {
  			return "" // pod validation should catch this on create
  		}
  
  		valueFrom, err := fieldpath.ExtractFieldPathAsString(pod, internalFieldPath)
  		if err != nil {
  			return "" // pod validation should catch this on create
  		}
  
  		return valueFrom
  	}
  }
docs: // EnvValueFrom is exported for use by describers in other packages