/**
  * Renders the HTML response text
  *
  * @return string
  */
 private function _getDisplay()
 {
     // The header may contain nothing at all,
     // if its content was already rendered
     // and, in this case, the header will be
     // in the content part of the request
     $retval = $this->_header->getDisplay();
     $retval .= $this->_HTML;
     $retval .= $this->_footer->getDisplay();
     return $retval;
 }