[FMX] Question about prototypes

Hello,

I’m not to keen on prototypes quite yet, but I have this code in frame one of my movie:
[AS]
MovieClip.prototype.fadein = function(max, speed) {
this.onEnterFrame = function() {
if (this._alpha<max) {
this._alpha += speed;
} else {
this._alpha = max;
delete this.onEnterFrame;
}
};
};
[/AS]

several frames later I have an MC with this code on it:
[AS]
onClipEvent(enterFrame){
this.fadein(100,3);
}
[/AS]

I would rather not have the code on the MC, but on the timeline instead. I’ve tried putting this on the main timeline:
[AS]
leftBox.fadein(100,3);
[/AS]
but it doesn’t do anything, the only way I can get the prototype to actually work is if i put it into an onClipEvent on an MC. Is there something wrong with my prototype thats not letting me call it from the main timeline? Do I have to use clip events on MC’s to make this work?