PHP似乎不适合使用XML字符串？

I am creating an application where a users draws shapes on a canvas and then saves and retrieves them from a database. The saving part works fine, now though, im trying to load this XML content, Thats where the troubles are starting.

Firstly a user has a list of documents they have created, when clicked it loads that document into the applicaiton to do this, i use the following code, firstly a javascript function which takes the ID of the document, then sends it to a PHP script which retrieves that documents data from a database. The PHP script than loads that documents data into a $_SESSION['data'] variable. Once done, it goes back to the javascript function which redirects the user to application page.

function loadDocument(docID){
    $.ajax({
        url: "load_a_document.php",
        type: "POST",     
        data: { 
            documentID: docID,
        }, 
        success: function(data) 
        {
            alert(data); //THIS DISPLAYS THE XML WITH NO PROBLEMS???
            window.location = "application.php";
        }      
    });
};

The PHP queries the database and retreives the name and XML content of the document, it then does this:

$_SESSION['document_Name'] = $doc_NAME;
$_SESSION['document_XML'] = $doc_DATA;

echo($_SESSION['document_XML']); //this is 'data' on the ajax success call

Now when the PHP is finished it echoes the php context, this shows up in the alert box in the success:{} of AJAX with no problems. Now it takes the user to the actual application which begins like so:

<?php 
session_start();

$document_Name = $_SESSION['document_Name'];
$document_Data = $_SESSION['document_XML'];
?>
<script>
    alert(" <?php echo $document_Name; ?> "); //WORKS FINE
    alert(" <?php echo $_SESSION['document_Name']; ?> ") //WORKS FINE

    //alert(" <?php echo $document_Data; ?> "); //STOPS THE PAGE LOADING
    //alert(" <?php echo $_SESSION['document_XML']; ?> ") //STOPS THE PAGE LOADING
</script>

Fetching the first two items, there are no problems, as soon as XML data is printer then their is a real problem. I dont understand why the loadDiagram() can alert () the XML but my application page cannot. Has the data been corrupted somehow?

Thanks for any feedback.

You probably have quotes in the string that's causing the problem. Try

alert(<?php echo json_encode($document_Data) ?>);