File.applicationStorageDirectory.resolvePath("my-config.xml");

var fs:FileStream = new FileStream();
fs.open(file, FileMode.WRITE);
fs.writeUTF(myXmlContent);
fs.close();

var prefsFile:File = File.applicationStorageDirectory;
prefsFile = prefsFile.resolvePath("preferences.xml");
stream = new FileStream();
stream.open(prefsFile, FileMode.WRITE);
stream.writeUTFBytes(outputStringXML);

var saveStr:String = xmlToSave.toXMLString();
var file:File = new File('app-storage:/data.xml');
var fs:FileStream = new FileStream();
fs.open(file, FileMode.WRITE);
fs.writeUTFBytes(saveStr);
fs.close();