parse XML file

i'm trying parse a user selected XML file and am completely stuck. i've read through the Javascript Tools Guide CS6 - XML Object Reference section several times, but i must be missing something. here is my XML:

<xml>          <comp>                    <name>My Comp</name>                    <width>1280</width>                    <height>720</height>                    <fps>24</fps>          </comp>          <layers>                    <layer value="Layer Name 1">1</layer>                    <layer value="Layer Name 2">2</layer>                    <layer value="Layer Name 3">3</layer>                    <layer value="Layer Name 4">4</layer>          </layers></xml>

and here is my script attempting to parse it:

var config = File.openDialog("Choose A Config File","XML:*.xml");if (config){          var xmlString = config.toString();          var myXML = new XML(xmlString);          alert(myXML.length);}else{          alert("Could not open file.");} 

i get a blank alert box. future thanks for the help.