code: function watchValidity() {
  		if( !unwatch ) {
  			unwatch = $scope.$watch(
  				function() {
  					var results = evaluateConstraints(ngModel.$modelValue, true);
  					return isValid(results);
  				},
  				function(newval, oldval) {
  					if( newval !== oldval ) {
  						ngModel.$validate();
  					}
  				}
  			);
  		}
  	}
docs: @ngdoc method
  @name egkyron.ValidateController#watchValidity
  
  @description
  Watch the validity of this model.
  
  Watches can be expensive, so it is made optional. A watch on the validity is
  required if the validity this field depends on others.