【正文】 if a key on the keyboard is pressed, the on (keyPress) event occurs. You can attach scripts to handle these events and add all the interactivity you desire. Clip events Within a movie clip, you may react to a number of clip events that are triggered when the user enters or exits the scene or interacts with the scene using the mouse or keyboard. You might, for example, load an external SWF file or JPG image into the movie clip when the user enters the scene, or allow the user’ s mouse movements to reposition elements in the scene. Frame events On a main or movie clip Timeline, a system event occurs when the playhead enters a keyframe— this is known as a frame event. Frame events are useful for triggering actions based on the passage of time (moving through the Timeline) or for interacting with elements that are currently visible on the stage. When you add a script to a keyframe, it is executed when the keyframe is reached during playback. A script attached to a frame is called a frame script. One of the most mon uses of frame scripts is to stop the playback when a certain keyframe is reached. This is done with the stop() function. You select a keyframe and then add the stop() function as a script element in the Actions panel. Once you’ ve stopped the movie at a certain keyframe, you need to take some action. You could, for example, use a frame script to dynamically update the value of a label, to manage the interaction of elements on the stage, and so on. For more information, see Chapter 5, “ Handling Events,” on page . Organizing ActionScript code You may attach scripts to keyframes and to object instances (movie clips, buttons, and other symbols). However, if your ActionScript code is scattered over many keyframes and object instances, debugging your application will be much more difficult. It will also be impossible to share your code between different Flash applications. Therefore, it’ s important to follow best practices for coding when you create ActionScript in Flash. Rather than attaching your scripts to elements like keyframes, movie clips, and buttons, you should respond to events by calling functions that reside in a central location. One method is to attach embedded ActionScript to the first or second frame of the Timeline whenever possible so you don’ t have to search through the FLA file to find all your code. A mon practice is to create a layer called actions and place your ActionScript code there. When you attach all your scripts to individual elements, you’ re embedding all your code in the FLA file. If sharing your code between other Flash applications is important to you, use the Script window or your favorite text editor to create an external ActionScript (AS) file. By creating an external file, you make your code more modular and well anized. As your project grows, this convenience bees much more useful than you might imagine. An external file aids debugging and also source control management if you’ re working on a project with other developers. To use the ActionScript code contained in an external AS file, you create a script within the FLA file and then use the include statement to access the code you’ ve stored externally, as shown in the following example: include ../core/ You can also use Ac