Sort AS3 XMLList in document order

In Actionscript 3, is there a way to sort the nodes (instances of type XML开发者_开发技巧) in an XMLList in document order (as defined in the XDM spec; "Informally, document order is the order in which nodes appear in the XML serialization of a document")? Alternately, is there a way to compare the document position of two nodes?

Here's a little example of what I mean. In the real case, the list is constructed by a much more complicated process and might have hundreds of nodes.

var x:XML = <a><b/><b/></a>;
var b0:XML = x.b[0];
var b1:XML = x.b[1];
var l:XMLList = new XMLList();
l += b1;
l += b0;
var sl:XMLList = documentSortFunction(l);
assertTrue(sl[0] === b0);

I'm not sure I have a lot of hope here, since it seems that ECMA-357 (E4X) doesn't really have a concept of document, much less document order.

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Well, here's a sketch of the answer I came up with. This hasn't been tested much yet, but I thought I'd record it before I forget to.

The idea is to implement a function to generate a string for a node, such that the order of the strings is the same as the order of the nodes.

protected function generateSortID(n:XML):String
{
    var ret:String = '';
    while (n != null && n.childIndex() > -1)
    {
        var s:String = '' + n.childIndex();
        ret = '0000000'.substring(s.length) + s + '!' + ret;
        n = n.parent();
    }
    return ret;
}

protected function compareNodePair(a:Array, b:Array):int
{
    var ai:String = a[0];
    var bi:String = b[0];
    if (ai < bi)
        return -1;
    else if (ai > bi)
        return 1;
    else
        return 0;
}

// all nodes in input list must be part of the same document.
protected function documentSortFunction(l:XMLList):XMLList
{
    var augArr:Array = [];
    for (var il:String in l)
        augArr.push([generateSortID(l[il]), l[il]]);
    augArr.sort(compareNodePair);
    var ret:XMLList = new XMLList();
    for (var ia:String in augArr)
        ret += augArr[ia][1];
    return ret;
}