How to send data through xml in as3

Code :-
=====

var respTxt:TextField = new TextField();
var myTextFormat:TextFormat = new TextFormat();
myTextFormat.size = 14;

var xmlString:String = "<?xml version='1.0' encoding='ISO-8859-1'?><root><value>63</value></root>";
var book:XML = new XML(xmlString);

var xmlResponse:XML;

var xmlURLReq:URLRequest = new URLRequest("processPHP.php");
xmlURLReq.data = book;
xmlURLReq.contentType = "text/xml";
xmlURLReq.method = URLRequestMethod.POST;

var xmlSendLoad:URLLoader = new URLLoader();
//xmlSendLoad.addEventListener(Event.COMPLETE, onComplete, false, 0, true);
//xmlSendLoad.addEventListener(IOErrorEvent.IO_ERROR, onIOError, false, 0, true);
xmlSendLoad.load(xmlURLReq);

function onComplete(evt:Event):void {
    try {
        xmlResponse = new XML(evt.target.data);
        respTxt.text = xmlResponse;
        removeEventListener(Event.COMPLETE, onComplete);
        removeEventListener(IOErrorEvent.IO_ERROR, onIOError);
    } catch (err:TypeError) {
        respTxt.text = "An error occured when communicating with server:\n" + err.message;
    }
    placeText();
}

function onIOError(evt:IOErrorEvent):void {
    respTxt.text = "An error occurred when attempting to load the XML.\n" + evt.text;
    placeText();
}

function placeText():void {
    respTxt.x = 15;
    respTxt.y = 15;
    respTxt.multiline = true;
    respTxt.autoSize = TextFieldAutoSize.LEFT;
    respTxt.setTextFormat(myTextFormat);
    addChild(respTxt);
}


processPHP.php :-
=============


<?php
$file = fopen("docq.xml", "w+") or die("Can't open XML file");

$xmlString = $HTTP_RAW_POST_DATA;

if(!fwrite($file, $xmlString))
{
    print "Error writing to XML-file";
}
print $xmlString."\n";

fclose($file);

?>


Out put XML  :-
===========


<root>
  <value>63</value>
</root>