code: func (pw *partitioningWalker) walkFn(path string, info os.FileInfo, err error) error {
  	if err != nil {
  		return err
  	}
  
  	relPath, err := pw.fsView.RelativePath(path)
  	if err != nil {
  		return err
  	}
  	if !pw.seen.Add(relPath) || relPath == "" {
  		// Either the file or directory was already walked, or empty string
  		// indicates skip.
  		return common.WalkFuncSkipFile(info)
  	}
  	if info.IsDir() {
  		return nil
  	}
  
  	item := &Item{
  		Path:    path,
  		RelPath: relPath,
  		Mode:    info.Mode(),
  		Size:    info.Size(),
  	}
  
  	switch {
  	case item.Mode&os.ModeSymlink == os.ModeSymlink:
  		pw.parts.links.AddItem(item)
  	case item.Size < archiveThreshold:
  		pw.parts.filesToArchive.AddItem(item)
  	default:
  		pw.parts.indivFiles.AddItem(item)
  	}
  	return nil
  }
docs: // walkFn implements filepath.WalkFunc, for use traversing a directory hierarchy to be isolated.
  // It accumulates files in pw.parts, partitioned into symlinks and files categorized by size.