function zen_fieldset($element) {
  if ($element['#collapsible']) {
    drupal_add_js('misc/collapse.js');

    if (!isset($element['#attributes']['class'])) {
      $element['#attributes']['class'] = '';
    }

    $element['#attributes']['class'] .= ' collapsible';
    if ($element['#collapsed']) {
     $element['#attributes']['class'] .= ' collapsed';
    }
  }
  # custom fieldset CSS class from element #title
  $css_class = "my-custom-class-";
  $css_class .= str_replace(" ","-",strtolower($element['#title']));
  # using transliteration module to convert non-ASCII character where available
  if(module_exists('transliteration')){
	# including Transliteration functions
	require_once(drupal_get_path('module', 'transliteration') .'/transliteration.inc');
	$css_class = transliteration_clean_filename($css_class);
  }

  $element['#attributes']['class'] .= (!empty($element['#attributes']['class']) ? " " : "") . $css_class;

  return '<fieldset' . drupal_attributes($element['#attributes']) .'>' . ($element['#title'] ? '<legend>'. $element['#title'] .'</legend>' : '') . ($element['#description'] ? '<div class="description">'. $element['#description'] .'</div>' : '') . $element['#children'] . $element['#value'] . "</fieldset>\n";
}