//setup the validation library, you can optionally pass in an 'options' object to configure the plug-in
ko.validation.init();

//start using it!
var myValue = ko.observable().extend({ required: true });

//oooh complexity
var myComplexValue = ko.observable().extend({ 
                     required: true,
                     minLength: 3,
                     pattern: {
                          message: 'Hey this doesnt match my pattern',
                          params: '^[A-Z0-9].$'
                     }
                 });

//or chaining if you like that
var myComplexValue = ko.observable()

myComplexValue.extend({ required: true })
            .extend({ minLength: 3 })
            .extend({ pattern: {
                 message: 'Hey this doesnt match my pattern',
                 params: '^[A-Z0-9].$'
            }});

//want to know if all of your ViewModel's properties are valid?
var myViewModel = ko.validatedObservable({
   property1: ko.observable().extend({ required: true }),
   property2: ko.observable().extend({ max: 10 })
});

console.log(myViewModel.isValid()); //false

myViewModel().property1('something');
myViewModel().property2(9);

console.log(myViewModel.isValid()); //true

var myObj = ko.observable('').extend({ required: true });

var myObj = ko.observable('').extend({ min: 2 });