code: public int asNode(XPathContext xctxt)
      throws javax.xml.transform.TransformerException
    {
      int current = xctxt.getCurrentNode();
      
      DTM dtm = xctxt.getDTM(current);
      
      return dtm.getFirstChild(current);
    }
docs: Return the first node out of the nodeset, if this expression is
  a nodeset expression.  This is the default implementation for
  nodesets.
  <p>WARNING: Do not mutate this class from this function!</p>
  @param xctxt The XPath runtime context.
  @return the first node out of the nodeset, or DTM.NULL.