In this article, we describe the directory structure used by yiiframework.com - the official Yii framework website. While this structure may look overly complicated for small projects or may not be optimal in some sense, we believe it is appropriate for medium or large projects in a team development environment. In fact, we have successfully used the similar structure in some other big projects.
The article Fixing extensions without modifying their code reminded me of another patching technique that I used. My conviction and a hard look on the web had led me to an article Redefine PHP class methods or class giving me a head start to do what I wanted: patching third party code without touching the original to allow easy upgrades.
This is a reference to be used for Model rule validation and is compiled from the Yii documentation and code. The purpose is to have all the information gathered in one place instead of scattered. This reference is not an intro.
See The Definitive Guide to Yii, Declaring Validation Rules for a tutorial.