public static IFluentContinuation <TViewModel, TPropertyValue> Valid <TViewModel, TPropertyValue>(
this IFluentOperator <TViewModel, TPropertyValue> instance, CustomValidator <TPropertyValue> customValidator)
where TViewModel : ViewModelBase
{
var implementerInstance = (FluentImplementer <TViewModel, TPropertyValue>)instance;
implementerInstance.EnsureContextCurrentPropertyIsNotNull();
implementerInstance.AddToken(ExpressionNode.CustomValidation(implementerInstance.Context.CurrentProperty, (value, token) => customValidator((TPropertyValue)value, token)));
return((IFluentContinuation <TViewModel, TPropertyValue>)instance);
}