Dynamic MCs and indexing them

Hello! I’m having a problem while assigning variables into dynamically-created MovieClips. Here’s a pseudo-code of what I’m trying to achieve.

var myArray:Array = [];

// Create a movieClip for each element in XML.

for each(var tempXML:XML in allXML.details){
   var myMC:MovieClip = new MovieClip();

   myMC.y = myArray.length * 20;
   // Line above easily changes the y value of the MC
   // because the y variable is already declared in the MC class

   myMC.indexNumber = myArray.length;
   // Line above does not pass indexNumber variable into myMC
   // How can I assign new variables into this MC?
   
   this.stage.addChild(myMC);
   myArray.push(myMC);
}

I need the movie clips to contain their index values as a variable within them. I’ve tried several approaches, including declaring the variable names within the MC itself, but that doesn’t work either.

I would be very grateful if anyone could help me achieve this, thanks!