how do I type cast 'root' so that it is available from every class I create that extends a MovieClip?

in main fla on frame: 
import MenuActions;
var menuMC:MenuActions=new MenuActions;
menuButtons.addChild(menuMC);
 
 
 
 
 
MenuActions.as
-----------------------------------
package {
	import flash.events.*;
	import flash.text.TextField;
	import flash.net.*;
	import flash.display.*;
	import flash.utils.getDefinitionByName;
	import flash.text.TextField;
	import flash.text.TextFormat;
	import flash.text.TextFieldAutoSize;
	import flash.events.MouseEvent;
	import flash.text.TextFormatAlign;
	import gs.*;
	import gs.easing.*;
 
 
	public class MenuActions extends MovieClip {
 
		public static var selectedButton:MenuButton;
		public static var i:Number=0;
		public static var totalMenuWidth:Number=0;
		public static var lastMenuButtonWidth:Number=0;
		public static var menuButtonSpacing:Number=10;
 
 
 
 
		public function MenuActions():void {
			//attach the menu button on the menu path
			for (i = 0; i < MainMenu.buttonCount; i++) {
 
				//create menu button
				var menuItem:MenuButton = new MenuButton();
 
				//set menu label text and position
				menuItem.buttonLabel.buttonLabelText.autoSize=TextFieldAutoSize.LEFT;
				menuItem.buttonLabel.buttonLabelText.text=MainMenu.menuButtons[i].Name;
 
				lastMenuButtonWidth=menuItem.buttonLabel.buttonLabelText.width;
				menuItem.x=totalMenuWidth;
				totalMenuWidth+=lastMenuButtonWidth+menuButtonSpacing;
				menuItem.rolloverElement.width=lastMenuButtonWidth;
 
				//set the menu button colors
				TweenLite.to(menuItem.buttonLabel, 0, {tint:GlobalVars.menuButtonColor});
				TweenLite.to(menuItem.rolloverElement, 0, {tint:GlobalVars.menuButtonRolloverColor});
 
				addChild(menuItem);
 
				//menuItem.addEventListener(MouseEvent.ROLL_OVER,playOver);
				//menuItem.addEventListener(MouseEvent.ROLL_OUT,playOut);
				//menuItem.addEventListener(MouseEvent.CLICK,goClick);
			}
			positionMenu();
 
		}
 
		function positionMenu():void {
			//set menu position
			MovieClip(root).site_holder.x = -200; 
		}
 
	}
}
 
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