Jonathan Snook has posted an update to a previous post about validating multiple input fields at the same time in a CakePHP application. This update changes the way the validation is handled and moves it over into a Behavior.
Using the new behavior is much like using the script as it was before. You can name the validation properties to include the action name and it'll automatically set that validation set as the default.
His behavior lets you define validation rules, both included in a default set and as callbacks. He includes an example of its use and the full code (all thirty lines of it) for the behavior itself.