code: function(model, field) {
        var callback, eventName;
        if (field) {
          eventName = 'change:' + field;
          callback = _.bind(this.__updateFormField, {
            formModel: this,
            field: field
          });
        } else {
          eventName = 'change';
          callback = this.__updateFormModel;
        }
        this.listenTo(model, eventName, callback);
        this.__currentUpdateEvents.push({model: model, eventName: eventName});
      }
docs: ************** Private methods **************// 
  Sets up a listener to update the form model if the model's field (or any field) changes.
  @param model {Backbone.Model} the object model from which this form model will start listen to changes
  @param [field] {String} the field name that it will start listening to. If no field is given, it will listen to the general 'change' event.
  @method __listenToModelField
  @private