code: func (f *Folder) getFolder(name string) *Folder {
  	if next, found := f.Folders[name]; found {
  		return next
  	}
  	next := newFolder(name)
  	f.Folders[name] = next
  	return next
  }
docs: // getFolder returns a direct sub-folder within this folder.
  // name MUST NOT include filepath separators. If there is no
  // such folder a new one is created with that name.