Why I can't call method on nativeApplication.applicationDescriptor in Javascript?

Question

Hi,

In my html file which is in Adobe AIR project, I write following code to get a reference to the application descriptor:

var appXML = air.NativeApplication.nativeApplication.applicationDescriptor;

The statement is executed successfully. I can see appXML is referenced to the runtime.XML object from debugger. And if I call alert(appXML), I could see the application descriptor content shown in the alert dialog.

But, if I try to call a method on appXML like appXML.namespace(), then error will be thrown said that:

TypeError: Value  does not allow function calls.

And so as every method I tried, all failed. But the same method call works well in Actionscript.

Anyone know why?