This snippet shows how to change the [jQuery validation](http://jquery.bassistance.de/validate/demo/milk/) plugin's validation rules dynamically:
```javascript
$(document).ready(function() {
// Setup the default validation rules
var validator = $('form').validate({
rules: {
username: {
required: true,
minlength: 2
}
}
};
// Drop-down selection changes validation rules
$('#account-type').change(function () {
// Get the jQuery validation plugin's settings
var settings = $('form').validate().settings;
// Modify validation settings
$.extend(true, settings, {
rules: {
// Add validation of year
"year": {
required: true,
min: 2010,
max: 2020,
number: true
},
// Remove validation of username
"username": {}
}
});
});
});
```
You can also use CSS classes to achieve the same:
```javascript
$('#channel-title').addClass("{required:true,messages:{required:'required field'}}")
$('#channel-title').removeClass("{required:true,messages:{required:'required field'}}")
```