Flash assigns a class to the movie clip symbol code

In Flash, select File > New, select Flash document from the list of file types, and then click OK.
Use the Ellipse tool to draw a circle on the stage.
Select the drawn circle and choose Modify > Convert to symbol.

In the Convert to Symbol dialog box, select movie clips as the behavior of the symbol and enter BALL_MC in the Name text box.
Select advanced to display these options if the linked options are not already displayed.
Select the Export for ActionScript option, and then type MoveRight in the class text box. Click OK.
Save the file as a ball.fla in the Balltest directory (the same directory that contains the moveright.as file).
Test the Flash document (Control > Test Movie).
Each time a single hit movie clip, it moves 20 pixels to the right.

If you create a component property for a class, and you want movie clips to inherit these component properties, you also need to do one step: Select the movie clip symbol in the library panel, select component definition from the Library pop-up menu, and then enter the new class name in the Class box.