How to add informations to my xml - AS3 - AIR

I'm loading an xml file name animals.xml

var urlLoader = new URLLoader();
urlLoader.addEventListener(Event.COMPLETE,onXMLLoaded);
var file:File = File.documentsDirectory.resolvePath("animals.xml");
var stream:FileStream = new FileStream();  
urlLoader.load(new  URLRequest(file.url));
 
function onXMLLoaded(e:Event):void{
       xml =  new XML(e.target.data);
     trace(xml..animal.@name[2]);
}

when I click on a button, it modifies the name of the cat by Garfield

click_btn.addEventListener(MouseEvent.CLICK, btn_clicked, false, 0, true);

function btn_clicked(event:MouseEvent):void {
    modifyName();
}
 
function modifyName():void{
    xml..animal.@name[2] = "GARFIELD";
    stream.open(file, FileMode.WRITE);
stream.writeUTFBytes(xml);
stream.close();
}

How can I, now, add new information to my xml ?

My XML is build like that :

<?xml version="1.0" encoding="UTF-8"?>
<animals>
        <animal  type="dog" name="Fido" age="2">Fido is a good  dog.</animal>
        <animal  type="dog" name="Ralph" age="1">Ralph is  brown.</animal>
        <animal  type="dog" name="Brian" age="1">Brian is  Ralph's brother.</animal>
        <animal  type="cat" name="Charlie" age="3">Charlie  likes fish.</animal>
      <animal type="rabit" name="Gulper" age="3">Gulper does  not want to be eaten.</animal>
</animals>

How do I do to add a new line ? For example :

animal type ="turtle"
name "Caroline"
age = "5"
Caroline is a turtle 

So, in the results, I'll have :

            <animal  type="dog" name="Fido" age="2">Fido is a good  dog.</animal>
            <animal  type="dog" name="Ralph" age="1">Ralph is  brown.</animal>
            <animal  type="dog" name="Brian" age="1">Brian is  Ralph's brother.</animal>
            <animal  type="cat" name="Charlie" age="3">Charlie  likes fish.</animal>
          <animal type="rabit" name="Gulper" age="3">Gulper does  not want to be eaten.</animal>
 <animal  type="turtle" name="Caroline" age="5"> Caroline is a turtle </animal>
    </animals>