self-referencing elements in XML

[Anshul.Mittal@iint.com]

I came across some self-referencing elements in xCBL3.0 (one of the example
is below).
   Is it legal to have self-referencing elements in XML ?
   I am having a major problem while I try to create a data structure using
WebMethods using this DTD....

     PackageReference (Element) (Namespace: XCBL30)
     Content: Quantity? ,  PackageIDReference (Type: int) ,
PackageReference?
     Description: The PackageReference element provides a reference for the packaging of the item.
     Quantity  is the quantity of the item in the referenced package.
     PackageIDReference  references the package ID of the package containing the item found in the PackageDetail element.
     PackageReference  provides a reference for the packaging of the item.

Any comments ?

Thanks
Anshul