Multiple business models contain objects whose properties must satisfy specific rules. For instance, a property value must be within a particular range. Applications with these business objects should have a mechanism that will control whether end-user data manipulations satisfy predefined rules. This mechanism should also support an administrator's rules modifications and other essential elements. The eXpressApp Framework provides the Validation module, containing all the necessary elements to build the user input validation mechanism into your applications. The concept used in this module is based on Rule and Context notions, and so, is called Contextual Validation. Topics in this section will familiarize you with this concept, and show you how to use it in your applications. You can see many examples of the Validation Module in use in the Validation section of the FeatureCenter demo, which is supplied with XAF. This demo is located in the %PUBLIC%\Documents\DevExpress Demos 18.2\Components\eXpressApp Framework\FeatureCenter folder, by default.