ActionScript 2.0 Language Reference - Adobe Help and Support

When a movie clip instance is placed by the Timeline or created using attachMovie() or
duplicateMovieClip(), ActionScript invokes the constructor for the appropriate class with
the keyword this pointing to the object. The constructor function is invoked with no
parameters.
If you use this method to register a movie clip with an ActionScript class other than
MovieClip, the movie clip symbol doesn't inherit the methods, properties, and events of the
built-in MovieClip class unless you include the MovieClip class in the prototype chain of the
new class. The following code creates a new ActionScript class called theClass that inherits
the properties of the MovieClip class:
theClass.prototype = new MovieClip();
Availability: ActionScript 1.0; Flash Player 6 - If you are using ActionScript 2.0 classes, you
can use the ActionScript 2.0 Class field in the Linkage Properties or Symbol Properties dialog
box to associate an object with a class instead of using this method.
Parameters
name:String - String; the linkage identifier of the movie clip symbol or the string identifier
for the ActionScript class.
theClass:Function - A reference to the constructor function of the ActionScript class or
null to unregister the symbol.
Returns
Boolean - A Boolean value: if the class registration succeeds, a value of true is returned;
false otherwise.
See also
attachMovie (MovieClip.attachMovie method), duplicateMovieClip
(MovieClip.duplicateMovieClip method)
1014 ActionScript classes