XML in ActionScript 2 class

I’ve just converted some code to an ActionScript 2 class, and now the XML doesn’t work.

class Menus.DropSlideMenu
	var _myXML;

	public function DropSlideMenu()
	function init()
		_myXML = new XML();
		_myXML.ignoreWhite = true;
		_myXML.onLoad = buildMenu;
	function buildMenu()
               trace(_myXML); // returns 'undefined':

The xml onLoad handler runs but the trace statement returns ‘undefined’.
The .FLA that uses this class looks like this:

import Menus.DropSlideMenu;

mytest = new DropSlideMenu();

Does anyone understand whats going on? I hope this is just a silly error because of the xmas booze.