code: func (h *Handler) servePermanodesWithAttr(rw http.ResponseWriter, req *http.Request) {
  	defer httputil.RecoverJSON(rw, req)
  	var wr WithAttrRequest
  	wr.fromHTTP(req)
  	res, err := h.GetPermanodesWithAttr(&wr)
  	if err != nil {
  		httputil.ServeJSONError(rw, err)
  		return
  	}
  	httputil.ReturnJSON(rw, res)
  }
docs: // servePermanodesWithAttr uses the indexer to search for the permanodes matching
  // the request.
  // The valid values for the "attr" key in the request (i.e the only attributes
  // for a permanode which are actually indexed as such) are "tag" and "title".