The source code

    /**
     * @class Ext.air.NativeObservable
     * @extends Ext.util.Observable
     *
     * Adds ability for Ext Observable functionality to proxy events for native (AIR) object wrappers
     *
     * @constructor
     */

    Ext.air.NativeObservable = Ext.extend(Ext.util.Observable, {
    	addListener : function(name){
    		this.proxiedEvents = this.proxiedEvents || {};
    		if(!this.proxiedEvents[name]){
    			var instance = this;
    			var f = function(){
    				var args = Array.prototype.slice.call(arguments, 0);
    				args.unshift(name);
    				instance.fireEvent.apply(instance, args);
    			};
    			this.proxiedEvents[name] = f;
    			this.getNative().addEventListener(name, f);
    		}
    		Ext.air.NativeObservable.superclass.addListener.apply(this, arguments);
    	}
    });

    Ext.air.NativeObservable.prototype.on = Ext.air.NativeObservable.prototype.addListener;