code: func (c *Manager) GetLibraryItemFile(ctx context.Context, id, fileName string) (*File, error) {
  	url := internal.URL(c, internal.LibraryItemFilePath).WithID(id).WithAction("get")
  	spec := struct {
  		Name string `json:"name"`
  	}{fileName}
  	var res File
  	return &res, c.Do(ctx, url.Request(http.MethodPost, spec), &res)
  }
docs: // GetLibraryItemFile returns a file with the provided name for a library item.