code: function listen(model, listener) {
      model.on('change', listener);
  
      model.values().forEach(function listenRecur(value) {
          var isCollection = value && value._byId;
  
          if (!isCollection) {
              return;
          }
  
          // for each collection listen to it
          // console.log('listenCollection')
          listenCollection(value, listener);
      });
  }
docs: listen to a Backbone model