code: public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
    {
  
      String s1 = m_arg0.execute(xctxt).str();
      String s2 = m_arg1.execute(xctxt).str();
  
      // Add this check for JDK consistency for empty strings.
      if (s1.length() == 0 && s2.length() == 0)
        return XBoolean.S_TRUE;
  
      int index = s1.indexOf(s2);
  
      return (index > -1) ? XBoolean.S_TRUE : XBoolean.S_FALSE;
    }
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