ActionSript 3 now allows you to specify default values for your function's parameters. In doing so, that parameter then becomes optional and the default value assigned to the respective argument in the function call if a value is explicitly not provided.

ActionScript Code:

function method(required:String, optional:String = "default"):void {
trace(required +" "+optional);
}
method("Hello"); // "Hello default"

You can only place parameters with default values after all required parameters. In other words you can't have

ActionScript Code:

// Incorrect:
function method(required:String = "default", optional:String):void { ...

since there would be no way for optional to be set without required having to be set as well.