code: public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
    {
  
      XMLString s1 = m_arg0.execute(xctxt).xstr();
      XMLString s2 = m_arg1.execute(xctxt).xstr();
      int index = s1.indexOf(s2);
  
      return (-1 == index)
             ? XString.EMPTYSTRING
             : (XString)s1.substring(index + s2.length());
    }
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