code: func EnableCrossGroupDecoding(d runtime.Decoder, sourceGroup, destGroup string) error {
  	internal, ok := d.(*codec)
  	if !ok {
  		return fmt.Errorf("unsupported decoder type")
  	}
  
  	dest, ok := internal.decodeVersion[destGroup]
  	if !ok {
  		return fmt.Errorf("group %q is not a possible destination group in the given codec", destGroup)
  	}
  	internal.decodeVersion[sourceGroup] = dest
  
  	return nil
  }
docs: // EnableCrossGroupDecoding modifies the given decoder in place, if it is a codec
  // from this package. It allows objects from one group to be auto-decoded into
  // another group. 'destGroup' must already exist in the codec.