code: func (dir *Directory) lookup(path string) *Directory {
  	d := splitPath(dir.Path)
  	p := splitPath(path)
  	i := 0
  	for i < len(d) {
  		if i >= len(p) || d[i] != p[i] {
  			return nil
  		}
  		i++
  	}
  	for dir != nil && i < len(p) {
  		dir = dir.lookupLocal(p[i])
  		i++
  	}
  	return dir
  }
docs: // lookup looks for the *Directory for a given path, relative to dir.