CFormatter is one of Yii's core components and used to format values displayed in widgets like CGridView or CDetailView. All classic formats like numbers, text, urls or datetime are supported but you may have to use a formatting rule that isn't built in. Let's say we want to display arrays of strings (like tags associated with a product model). When using CDetailView we would usually make use of PHPs implode function to create a simple string value of all values in the $product->tags array.
If you are lucky enough and have the privilege to develop on a Linux based environment, this little tip might boost-up your TDD process (at least the Unit Testing part). Please note, that this should work just fine with Apple computers also, but not tested!