Are self-referencing elements legal 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 problems while I try to create a data structure using
WebMethods using this DTD as the tool is going in infinite loop due to
these self-referencing elements.

          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 input ?

Thanks
Anshul