code: func (r *NetworkInterfaceSubresource) ValidateDiff() error {
  	log.Printf("[DEBUG] %s: Beginning diff validation", r)
  
  	// Ensure that network resource allocation options are only set on vSphere
  	// 6.0 and higher.
  	version := viapi.ParseVersionFromClient(r.client)
  	if version.Older(viapi.VSphereVersion{Product: version.Product, Major: 6}) {
  		if err := r.restrictResourceAllocationSettings(); err != nil {
  			return err
  		}
  	}
  
  	log.Printf("[DEBUG] %s: Diff validation complete", r)
  	return nil
  }
docs: // ValidateDiff performs any complex validation of an individual
  // network_interface sub-resource that can't be done in schema alone.