A behavior is a combination of a trigger paired with an effect. A trigger is an action, such as a mouse click on a component, a component getting focus, or a component becoming visible. An effect is a visible or audible change to a target component that occurs over a period of time, measured in milliseconds. Examples of effects are fading, resizing, or moving a component. You can define multiple effects for a single trigger.

By default, Flex components don't play an effect when a trigger occurs. To configure a component to use an effect, you associate an effect with the trigger.

Triggers are not ActionScript events. For example, a Button control has both a mouseDownEffect trigger and a mouseDown event. The trigger initiates a Flex effect; the event calls an ActionScript function or object method.

For more information, see Using Behaviors in the Adobe Flex 3 Developer Guide.