Behaviors are instances of yiiaseBehavior, or of a child class. Behaviors, also known as mixins, allow you to enhance the functionality of an existing component class without needing to change the class's inheritance. Attaching a behavior to a component "injects" the behavior's methods and properties into the component, making those methods and properties accessible as if they were defined in the component class itself. Moreover, a behavior can respond to the events triggered by the component, which allows behaviors to also customize the normal code execution of the component.