A common source of confusion among new Yii users is how the 'safe' validator works, how it works with other validators, and why it's necessary in the first place. This article means to clear up this confusion, as well as explain the notion of Massive Assignment.
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.
When you're filling up a form of a CActiveRecord (using CActiveForm for example), usually you'll construct your code so that in case of validation error you'll get back the form with the error displayed back to you, typically when CActiveForm.errorSummary() is used. This is how its done by Gii.