code: protected XMLString getArg0AsString(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
      if(null == m_arg0)
      {
        int currentNode = xctxt.getCurrentNode();
        if(DTM.NULL == currentNode)
          return XString.EMPTYSTRING;
        else
        {
          DTM dtm = xctxt.getDTM(currentNode);
          return dtm.getStringValue(currentNode);
        }
        
      }
      else
        return m_arg0.execute(xctxt).xstr();   
    }
docs: Execute the first argument expression that is expected to return a
  string.  If the argument is null, then get the string value from the
  current context node.
  
  @param xctxt Runtime XPath context.
  
  @return The string value of the first argument, or the string value of the
  current context node if the first argument is null.
  
  @throws javax.xml.transform.TransformerException if an error occurs while
  executing the argument expression.