Behaviors lets you add functionality to user interface controls without having to subclass them. Behaviors are written in code and added to controls in XAML or code.
Behaviors enable you to implement code that you would normally have to write as code-behind, because it directly interacts with the API of the control in such a way that it can be concisely attached to the control. This article provides an introduction to behaviors.
Attached behaviors are
static classes with one or more attached properties. This article demonstrates how to create and consume attached behaviors.
Behaviors are reusable across more than one application. These articles explain how to create useful behaviors to perform commonly used functionality.