Accessing vars in SuperClass from SubClass

So, how would you create a class that can access a variable in the class where the subClass was created(superclass), I realise this might be unclear so in example


package  {
import flash.display.MovieClip;
public class Main extends MovieClip {
public var demoString:String = "TEST";
public static var newClass:SubClass;
public function Main() {           
// constructor code           
 init();        
}        
public function init():void{     
newClass = new SubClass();     
     } 
   }
 }

package  {
public class SubClass extends Main{    
public function SubClass() {
// constructor code            
trace(super(demoString));        
   }    
  }
}

I cant read demoString from the SuperClass and when I try and test this code I get this error?
Error: Error #2136: The SWF file file:///C|/Users/classes/Main.swf contains invalid data.
at Main/init()
at Main()