code: public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
    {
  
      String name = m_arg0.execute(xctxt).str();
      int context = xctxt.getCurrentNode();
      DTM dtm = xctxt.getDTM(context);
      int doc = dtm.getDocument();
      
      String uri = dtm.getUnparsedEntityURI(name);
  
      return new XString(uri);
    }
docs: Execute the function.  The function must return
  a valid object.
  @param xctxt The current execution context.
  @return A valid XObject.
  
  @throws javax.xml.transform.TransformerException