Index: modules/system/system.js
===================================================================
RCS file: modules/system/system.js
diff -N modules/system/system.js
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ modules/system/system.js	17 Jan 2007 00:43:40 -0000
@@ -0,0 +1,34 @@
+// $Id$
+
+/**
+ * Show/hide custom format sections on the date-time settings page.
+ */
+Drupal.dateTimeAutoAttach = function() {
+  $("#edit-date-format-short").change(function() {
+    if ($(this).val() == 'custom') {
+      $("#short-custom-div").show();
+    }
+    else {
+      $("#short-custom-div").hide();
+    }
+  });
+ $("#edit-date-format-medium").change(function() {
+    if ($(this).val() == 'custom') {
+      $("#medium-custom-div").show();
+    }
+    else {
+      $("#medium-custom-div").hide();
+    }
+  });
+ $("#edit-date-format-long").change(function() {
+    if ($(this).val() == 'custom') {
+      $("#long-custom-div").show();
+    }
+    else {
+      $("#long-custom-div").hide();
+    }
+  });
+  $("#edit-date-format-short").trigger("change");
+  $("#edit-date-format-medium").trigger("change");
+  $("#edit-date-format-long").trigger("change");
+}
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.441
diff -u -p -r1.441 system.module
--- modules/system/system.module	15 Jan 2007 12:03:50 -0000	1.441
+++ modules/system/system.module	17 Jan 2007 00:43:40 -0000
@@ -778,6 +778,14 @@ function system_rss_feeds_settings() {
 }
 
 function system_date_time_settings() {
+  drupal_add_js(drupal_get_path('module', 'system') .'/system.js', 'module');
+  drupal_add_js('
+// Global Killswitch
+if (Drupal.jsEnabled) {
+  $(document).ready(function() {
+    Drupal.dateTimeAutoAttach();
+  });
+}', 'inline');
   // Date settings:
   $zones = _system_zonelist();
 
@@ -804,6 +812,8 @@ function system_date_time_settings() {
     $datelongchoices[$f] = format_date(time(), 'custom', $f);
   }
 
+  $datelongchoices['custom'] = $datemediumchoices['custom'] = $dateshortchoices['custom'] = t('Custom format');
+
   $form['date_default_timezone'] = array(
     '#type' => 'select',
     '#title' => t('Default time zone'),
@@ -820,30 +830,60 @@ function system_date_time_settings() {
     '#description' => t('Enable or disable user-configurable time zones. When enabled, users can set their own time zone and dates will be updated accordingly.')
   );
 
+  $date_format_short = variable_get('date_format_short', $dateshort[1]);
   $form['date_format_short'] = array(
     '#type' => 'select',
     '#title' => t('Short date format'),
-    '#default_value' => variable_get('date_format_short', $dateshort[1]),
+    '#default_value' => (isset($dateshortchoices[$date_format_short])? $date_format_short : 'custom'),
     '#options' => $dateshortchoices,
     '#description' => t('The short format of date display.')
   );
 
+  $form['date_format_short_custom'] = array(
+    '#prefix' => '<div id="short-custom-div">',
+    '#suffix' => '</div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom short date format'),
+    '#default_value' => variable_get('date_format_short_custom', ''),
+    '#description' => t('A user-defined short date format.') . (variable_get('date_format_short_custom', '') === ''? '' : t(' This format is currently set to display as %date.', array('%date' => date(variable_get('date_format_short_custom', ''))))),
+  );
+
+  $date_format_medium = variable_get('date_format_medium', $datemedium[1]);
   $form['date_format_medium'] = array(
     '#type' => 'select',
     '#title' => t('Medium date format'),
-    '#default_value' => variable_get('date_format_medium', $datemedium[1]),
+    '#default_value' => (isset($datemediumchoices[$date_format_medium])? $date_format_medium : 'custom'),
     '#options' => $datemediumchoices,
     '#description' => t('The medium sized date display.')
   );
 
+  $form['date_format_medium_custom'] = array(
+    '#prefix' => '<div id="medium-custom-div">',
+    '#suffix' => '</div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom medium date format'),
+    '#default_value' => variable_get('date_format_medium_custom', ''),
+    '#description' => t('A user-defined medium date format.') . (variable_get('date_format_medium_custom', '') === ''? '' : t(' This format is currently set to display as %date.', array('%date' => date(variable_get('date_format_medium_custom', ''))))),
+  );
+
+  $date_format_long = variable_get('date_format_long', $datelong[0]);
   $form['date_format_long'] = array(
     '#type' => 'select',
     '#title' => t('Long date format'),
-    '#default_value' => variable_get('date_format_long', $datelong[0]),
+    '#default_value' => (isset($datelongchoices[$date_format_long])? $date_format_long : 'custom'),
     '#options' => $datelongchoices,
     '#description' => t('Longer date format used for detailed display.')
   );
 
+  $form['date_format_long_custom'] = array(
+    '#prefix' => '<div id="long-custom-div">',
+    '#suffix' => '</div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom long date format'),
+    '#default_value' => variable_get('date_format_long_custom', ''),
+    '#description' => t('A user-defined long date format.') . (variable_get('date_format_long_custom', '') === ''? '' : t(' This format is currently set to display as %date.', array('%date' => date(variable_get('date_format_long_custom', ''))))),
+  );
+
   $form['date_first_day'] = array(
     '#type' => 'select',
     '#title' => t('First day of week'),
@@ -855,6 +895,18 @@ function system_date_time_settings() {
   return system_settings_form($form);
 }
 
+function system_date_time_settings_validate($form_id, $form_values) {
+  if ($form_values['date_format_short'] == 'custom') {
+    $form_values['date_format_short'] = $form_values['date_format_short_custom'];
+  }
+  if ($form_values['date_format_medium'] == 'custom') {
+    $form_values['date_format_medium'] = $form_values['date_format_medium_custom'];
+  }
+  if ($form_values['date_format_long'] == 'custom') {
+    $form_values['date_format_long'] = $form_values['date_format_long_custom'];
+  }
+}
+
 function system_site_maintenance_settings() {
 
   $form['site_offline'] = array(