code: function(model, field, computedAlias) {
        var callback, eventName;
        if (field) {
          eventName = 'change:' + field;
        } else {
          eventName = 'change';
        }
        callback = _.bind(this.__invokeComputedPull, {
          formModel: this,
          alias: computedAlias
        });
        this.listenTo(model, eventName, callback);
        this.__currentUpdateEvents.push({model: model, eventName: eventName});
      }
docs: Sets up a listener on one (or all) of the fields that is needed to update a computed value
  @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.
  @param computedAlias {String} the name/alias of the computed mapping being used.
  @method __listenToComputedValuesDependency
  @private