code: public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
    {
  
      StringBuffer sb = new StringBuffer();
  
      // Compiler says we must have at least two arguments.
      sb.append(m_arg0.execute(xctxt).str());
      sb.append(m_arg1.execute(xctxt).str());
  
      if (null != m_arg2)
        sb.append(m_arg2.execute(xctxt).str());
  
      if (null != m_args)
      {
        for (int i = 0; i < m_args.length; i++)
        {
          sb.append(m_args[i].execute(xctxt).str());
        }
      }
  
      return new XString(sb.toString());
    }
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