code: func (pm *PodManifest) assertValid() error {
  	if pm.ACKind != PodManifestKind {
  		return pmKindError
  	}
  
  	// ensure volumes names are unique (unique key)
  	volNames := make(map[types.ACName]bool, len(pm.Volumes))
  	for _, vol := range pm.Volumes {
  		if volNames[vol.Name] {
  			return fmt.Errorf("duplicate volume name %q", vol.Name)
  		}
  		volNames[vol.Name] = true
  	}
  	return nil
  }
docs: // assertValid performs extra assertions on an PodManifest to
  // ensure that fields are set appropriately, etc. It is used exclusively when
  // marshalling and unmarshalling an PodManifest. Most
  // field-specific validation is performed through the individual types being
  // marshalled; assertValid() should only deal with higher-level validation.