docs: function(jid_or_user_id) {
          var jid;
          if (typeof jid_or_user_id === 'string') {
              jid = jid_or_user_id;
          } else if (typeof jid_or_user_id === 'number') {
              jid = jid_or_user_id + '-' + config.creds.appId + '@' + config.endpoints.chat;
          } else {
              throw new Error('The method "jidOrUserId" may take jid or id');
          }
          return jid;
      }