Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.426
diff -u -p -r1.426 form.inc
--- includes/form.inc	8 Jan 2010 06:36:34 -0000	1.426
+++ includes/form.inc	8 Jan 2010 16:35:37 -0000
@@ -2391,6 +2391,20 @@ function form_pre_render_conditional_for
   return $element;
 }
 
+function form_pre_render_container($element) {
+  // Apply CSS classes based on the original element's #type.
+  if (isset($element['#type'])) {
+    $element['#attributes']['class'][] = drupal_html_class('form-type-' . $element['#type']);
+  }
+  if (isset($element['#name'])) {
+    $element['#attributes']['class'][] = drupal_html_class('form-type-' . $element['#name']);
+  }
+  // Convert this element into a wrapping container.
+  $element['#type'] = 'container';
+
+  return $element;
+}
+
 function form_process_checkboxes($element) {
   $value = is_array($element['#value']) ? $element['#value'] : array();
   $element['#tree'] = TRUE;
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.871
diff -u -p -r1.871 system.module
--- modules/system/system.module	8 Jan 2010 06:36:34 -0000	1.871
+++ modules/system/system.module	8 Jan 2010 16:35:38 -0000
@@ -383,7 +383,7 @@ function system_element_info() {
     '#input' => TRUE,
     '#process' => array('form_process_radios'),
     '#theme_wrappers' => array('radios'),
-    '#pre_render' => array('form_pre_render_conditional_form_element'),
+    '#pre_render' => array('form_pre_render_conditional_form_element', 'form_pre_render_container'),
   );
   $types['radio'] = array(
     '#input' => TRUE,
@@ -398,7 +398,7 @@ function system_element_info() {
     '#tree' => TRUE,
     '#process' => array('form_process_checkboxes'),
     '#theme_wrappers' => array('checkboxes'),
-    '#pre_render' => array('form_pre_render_conditional_form_element'),
+    '#pre_render' => array('form_pre_render_conditional_form_element', 'form_pre_render_container'),
   );
   $types['checkbox'] = array(
     '#input' => TRUE,