This article is called extended guide is because there is already a security guide in the Yii tutorial security section. but that guide is not complete in the sense that it does not rise the developers' attention to some other commonly happening attacks: SQL injection and magic URL, which can be major vulnerabilities in your application without much caring.
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.
Sometimes the active form we wish to use to edit/add a new element on our database is too small and we believe that is much better to use an AJAX'ed dialog/slide form rather than reloading the page to just display one or two fields.