parse() can't accept a "<html>" element

```
var myDoc = "<html>
    <head><title>My Title</title></head>
    <body>My Body</body>
</html>".parse();
```

   trace (myDoc.length);

This shows 5.  TextNode, head, TextNode, body, TextNode.

I would expect it to show 1: html

If we change `<html></html>` to `<myxml></myxml>`, it works as expected.

Tested in Firefox
