Flex includes a component-based development model that you use to develop your application and its user interface. You can use the prebuilt visual components included with Flex, extend components to add new properties and methods, and create components as required by your application.

Visual components are extremely flexible and provide you with a great deal of control over the component's appearance, how the component responds to user interactions, the font and size of any text included in the component, the size of the component in the application, and many other characteristics.

The characteristics of visual components include the following:

Size 

Height and width of a component. All visual components have a default size. You can use the default size, specify your own size, or let Flex resize a component as part of laying out your application.

Events 

Application or user actions that require a component response. Events include component creation, mouse actions such as moving the mouse over a component, and button clicks.

Styles 

Characteristics such as font, font size, and text alignment. These are the same styles that you define and use with Cascading Style Sheets (CSS).

Behaviors 

Visible or audible changes to the component triggered by an application or user action. Examples of behaviors are moving or resizing a component based on a mouse click.

Skins 

Classes that control a visual component's appearance.