To extend the functionality of you web application relative to your requirements you are supposed to use existing yii core libraries or use external libraries. There are some steps to ensure security, uniqueness, modularity, performance and to avoid rework in future.
Sometime its very important to perform many actions/operation with limited time frame for friendly use, select2 provides a lot of such functionality , I just extend it tags functionality to provide a quick use for developer to save time, as I spent much time on it.
By Integrating the Zend 2.* framework into Yii you can quickly and painlessly generate XML outputs from your controllers. This will be helpful to anyone who has never done this before or only done it with Zend 1 as the introduction of namespaces can be strange when you first view them.