Index: modules/system/admin.css
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/admin.css,v
retrieving revision 1.12
diff -u -p -r1.12 admin.css
--- modules/system/admin.css	23 Nov 2006 11:05:46 -0000	1.12
+++ modules/system/admin.css	19 Mar 2007 23:00:34 -0000
@@ -96,4 +96,28 @@ table.system-status-report tr.ok th {
 }
 .theme-settings-bottom {
   clear: both;
-}
\ No newline at end of file
+}
+
+/*
+** Date and time settings page
+*/
+div.date-container {
+  overflow: auto;
+}
+
+div.date-container > div {
+  float: left;
+}
+
+html.js div.custom-container {
+  display: none;
+}
+
+html.js div.custom-container .form-item label {
+  visibility: hidden;
+}
+
+div.custom-container {
+  margin-left: 15px;
+  width: 50%;
+}
Index: modules/system/system.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.js,v
retrieving revision 1.1
diff -u -p -r1.1 system.js
--- modules/system/system.js	13 Feb 2007 07:41:51 -0000	1.1
+++ modules/system/system.js	19 Mar 2007 23:00:34 -0000
@@ -22,3 +22,25 @@ Drupal.cleanURLsSettingsCheck = function
     }
   }});
 }
+
+/**
+ * Show/hide custom format sections on the date-time settings page.
+ */
+Drupal.dateTimeAutoAttach = function() {
+  // Show/hide custom format depending on the select's value.
+  $("select.date-format").change(function() {
+    $(this).parents("div.date-container").children("div.custom-container")[$(this).val() == "custom" ? "show" : "hide"]();
+  });
+
+  // Attach keyup handler to custom format inputs.
+  $("input.custom-format").keyup(function() {
+    var input = $(this);
+    var url = Drupal.settings.dateTime.lookup +(Drupal.settings.dateTime.lookup.match(/\?q=/) ? "&format=" : "?q=") + Drupal.encodeURIComponent(input.val());
+    $.getJSON(url, function(data) {
+      $("div.description span", input.parent()).html(data);
+    });
+  });
+
+  // Trigger the event handler to show the form input if necessary.
+  $("select.date-format").trigger("change");
+}
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.457
diff -u -p -r1.457 system.module
--- modules/system/system.module	17 Mar 2007 18:30:14 -0000	1.457
+++ modules/system/system.module	19 Mar 2007 23:00:34 -0000
@@ -243,6 +243,11 @@ function system_menu() {
     'page callback' => 'drupal_get_form',
     'page arguments' => array('system_date_time_settings'),
   );
+  $items['admin/settings/date-time/lookup'] = array(
+    'title' => t('Date and time lookup'),
+    'type' => MENU_CALLBACK,
+    'page callback' => 'system_date_time_lookup',
+  );
   $items['admin/settings/site-maintenance'] = array(
     'title' => t('Site maintenance'),
     'description' => t('Take the site off-line for maintenance or bring it back online.'),
@@ -774,32 +779,41 @@ function system_rss_feeds_settings() {
 }
 
 function system_date_time_settings() {
+  drupal_add_js(drupal_get_path('module', 'system') .'/system.js', 'module');
+  drupal_add_js(array('dateTime' => array('lookup' => url('admin/settings/date-time/lookup'))), 'setting');
+  drupal_add_js('
+// Global Killswitch
+if (Drupal.jsEnabled) {
+  $(document).ready(Drupal.dateTimeAutoAttach);
+}', 'inline');
   // Date settings:
   $zones = _system_zonelist();
 
   // Date settings: possible date formats
-  $dateshort = array('Y-m-d H:i', 'm/d/Y - H:i', 'd/m/Y - H:i', 'Y/m/d - H:i',
+  $date_short = array('Y-m-d H:i', 'm/d/Y - H:i', 'd/m/Y - H:i', 'Y/m/d - H:i',
            'd.m.Y - H:i', 'm/d/Y - g:ia', 'd/m/Y - g:ia', 'Y/m/d - g:ia',
            'M j Y - H:i', 'j M Y - H:i', 'Y M j - H:i',
            'M j Y - g:ia', 'j M Y - g:ia', 'Y M j - g:ia');
-  $datemedium = array('D, Y-m-d H:i', 'D, m/d/Y - H:i', 'D, d/m/Y - H:i',
+  $date_medium = array('D, Y-m-d H:i', 'D, m/d/Y - H:i', 'D, d/m/Y - H:i',
           'D, Y/m/d - H:i', 'F j, Y - H:i', 'j F, Y - H:i', 'Y, F j - H:i',
           'D, m/d/Y - g:ia', 'D, d/m/Y - g:ia', 'D, Y/m/d - g:ia',
           'F j, Y - g:ia', 'j F Y - g:ia', 'Y, F j - g:ia', 'j. F Y - G:i');
-  $datelong = array('l, F j, Y - H:i', 'l, j F, Y - H:i', 'l, Y,  F j - H:i',
+  $date_long = array('l, F j, Y - H:i', 'l, j F, Y - H:i', 'l, Y,  F j - H:i',
         'l, F j, Y - g:ia', 'l, j F Y - g:ia', 'l, Y,  F j - g:ia', 'l, j. F Y - G:i');
 
   // Date settings: construct choices for user
-  foreach ($dateshort as $f) {
-    $dateshortchoices[$f] = format_date(time(), 'custom', $f);
+  foreach ($date_short as $f) {
+    $date_short_choices[$f] = format_date(time(), 'custom', $f);
   }
-  foreach ($datemedium as $f) {
-    $datemediumchoices[$f] = format_date(time(), 'custom', $f);
+  foreach ($date_medium as $f) {
+    $date_medium_choices[$f] = format_date(time(), 'custom', $f);
   }
-  foreach ($datelong as $f) {
-    $datelongchoices[$f] = format_date(time(), 'custom', $f);
+  foreach ($date_long as $f) {
+    $date_long_choices[$f] = format_date(time(), 'custom', $f);
   }
 
+  $date_long_choices['custom'] = $date_medium_choices['custom'] = $date_short_choices['custom'] = t('Custom format');
+
   $form['date_default_timezone'] = array(
     '#type' => 'select',
     '#title' => t('Default time zone'),
@@ -816,30 +830,75 @@ 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', $date_short[1]);
   $form['date_format_short'] = array(
+    '#prefix' => '<div class="date-container"><div>',
+    '#suffix' => '</div>',
     '#type' => 'select',
     '#title' => t('Short date format'),
-    '#default_value' => variable_get('date_format_short', $dateshort[1]),
-    '#options' => $dateshortchoices,
-    '#description' => t('The short format of date display.')
+    '#attributes' => array('class' => 'date-format'),
+    '#default_value' => (isset($date_short_choices[$date_format_short]) ? $date_format_short : 'custom'),
+    '#options' => $date_short_choices,
+    '#description' => t('The short format of date display.'),
   );
 
+  $default_short_custom = variable_get('date_format_short_custom', (isset($date_short_choices[$date_format_short]) ? $date_format_short : '')); 
+  $form['date_format_short_custom'] = array(
+    '#prefix' => '<div class="custom-container">',
+    '#suffix' => '</div></div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom short date format'),
+    '#attributes' => array('class' => 'custom-format'),
+    '#default_value' => $default_short_custom,
+    '#description' => t('A user-defined short date format. See the <a href="@url">PHP manual</a> for available options. This format is currently set to display as <span>%date</span>.', array('@url' => 'http://php.net/manual/function.date.php', '%date' => format_date(time(), 'custom', $default_short_custom))),
+  );
+
+  $date_format_medium = variable_get('date_format_medium', $date_medium[1]);
   $form['date_format_medium'] = array(
+    '#prefix' => '<div class="date-container"><div>',
+    '#suffix' => '</div>',
     '#type' => 'select',
     '#title' => t('Medium date format'),
-    '#default_value' => variable_get('date_format_medium', $datemedium[1]),
-    '#options' => $datemediumchoices,
-    '#description' => t('The medium sized date display.')
+    '#attributes' => array('class' => 'date-format'),
+    '#default_value' => (isset($datemediumchoices[$date_format_medium]) ? $date_format_medium : 'custom'),
+    '#options' => $date_medium_choices,
+    '#description' => t('The medium sized date display.'),
+  );
+
+  $default_medium_custom = variable_get('date_format_medium_custom', (isset($date_medium_choices[$date_format_medium]) ? $date_format_medium : ''));
+  $form['date_format_medium_custom'] = array(
+    '#prefix' => '<div class="custom-container">',
+    '#suffix' => '</div></div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom medium date format'),
+    '#attributes' => array('class' => 'custom-format'),
+    '#default_value' => $default_medium_custom,
+    '#description' => t('A user-defined medium date format. See the <a href="@url">PHP manual</a> for available options. This format is currently set to display as <span>%date</span>.', array('@url' => 'http://php.net/manual/function.date.php', '%date' => format_date(time(), 'custom', $default_medium_custom))),
   );
 
+  $date_format_long = variable_get('date_format_long', $date_long[0]);
   $form['date_format_long'] = array(
+    '#prefix' => '<div class="date-container"><div>',
+    '#suffix' => '</div>',
     '#type' => 'select',
     '#title' => t('Long date format'),
-    '#default_value' => variable_get('date_format_long', $datelong[0]),
-    '#options' => $datelongchoices,
+    '#attributes' => array('class' => 'date-format'),
+    '#default_value' => (isset($date_long_choices[$date_format_long]) ? $date_format_long : 'custom'),
+    '#options' => $date_long_choices,
     '#description' => t('Longer date format used for detailed display.')
   );
 
+  $default_long_custom = variable_get('date_format_long_custom', (isset($date_long_choices[$date_format_long]) ? $date_format_long : ''));
+  $form['date_format_long_custom'] = array(
+    '#prefix' => '<div class="custom-container">',
+    '#suffix' => '</div></div>',
+    '#type' => 'textfield',
+    '#title' => t('Custom long date format'),
+    '#attributes' => array('class' => 'custom-format'),
+    '#default_value' => $default_long_custom,
+    '#description' => t('A user-defined long date format. See the <a href="@url">PHP manual</a> for available options. This format is currently set to display as <span>%date</span>.', array('@url' => 'http://php.net/manual/function.date.php', '%date' => format_date(time(), 'custom', $default_long_custom))),
+  );
+
   $form['date_first_day'] = array(
     '#type' => 'select',
     '#title' => t('First day of week'),
@@ -851,6 +910,29 @@ function system_date_time_settings() {
   return system_settings_form($form);
 }
 
+function system_date_time_settings_submit($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'] = $form_values['date_format_long_custom'];
+  }
+  return system_settings_form_submit($form_id, $form_values);
+}
+
+/**
+ * Return the date for a given format string via Ajax.
+ */
+function system_date_time_lookup() {
+  $format = isset($_GET['format']) ? $_GET['format'] : array_pop(array_slice(explode('&', $_GET['q'], 2), 1));
+  $result = format_date(time(), 'custom', $format);
+  echo drupal_to_js($result);
+  exit;
+}
+
 function system_site_maintenance_settings() {
 
   $form['site_offline'] = array(
