Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1222
diff -u -p -F '^f' -r1.1222 common.inc
--- includes/common.inc	17 Sep 2010 14:53:21 -0000	1.1222
+++ includes/common.inc	17 Sep 2010 23:36:07 -0000
@@ -3070,6 +3070,12 @@ function drupal_pre_render_styles($eleme
   // URL changed.
   $query_string = variable_get('css_js_query_string', '0');
 
+  // For inline CSS to validate as XHTML, all CSS containing XHTML needs to be
+  // wrapped in CDATA. To make that backwards compatible with HTML 4, we need to
+  // comment out the CDATA-tag.
+  $embed_prefix = "\n<!--/*--><![CDATA[/*><!--*/\n";
+  $embed_suffix = "\n/*]]>*/-->\n";
+
   // Defaults for LINK and STYLE elements.
   $link_element_defaults = array(
     '#type' => 'html_tag',
@@ -3157,6 +3163,8 @@ function drupal_pre_render_styles($eleme
         if (isset($group['data'])) {
           $element = $style_element_defaults;
           $element['#value'] = $group['data'];
+          $element['#value_prefix'] = $embed_prefix;
+          $element['#value_suffix'] = $embed_suffix;
           $element['#attributes']['media'] = $group['media'];
           $element['#browsers'] = $group['browsers'];
           $elements[] = $element;
@@ -3165,6 +3173,8 @@ function drupal_pre_render_styles($eleme
           foreach ($group['items'] as $item) {
             $element = $style_element_defaults;
             $element['#value'] = $item['data'];
+            $element['#value_prefix'] = $embed_prefix;
+            $element['#value_suffix'] = $embed_suffix;
             $element['#attributes']['media'] = $item['media'];
             $element['#browsers'] = $group['browsers'];
             $elements[] = $element;
Index: modules/simpletest/tests/common.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/common.test,v
retrieving revision 1.126
diff -u -p -F '^f' -r1.126 common.test
--- modules/simpletest/tests/common.test	16 Sep 2010 20:14:49 -0000	1.126
+++ modules/simpletest/tests/common.test	17 Sep 2010 23:36:11 -0000
@@ -654,7 +654,7 @@ class CascadingStylesheetsTestCase exten
    */
   function testRenderInlinePreprocess() {
     $css = 'body { padding: 0px; }';
-    $css_preprocessed = '<style type="text/css" media="all">' . drupal_load_stylesheet_content($css, TRUE) . '</style>';
+    $css_preprocessed = '<style type="text/css" media="all">' . "\n<!--/*--><![CDATA[/*><!--*/\n" . drupal_load_stylesheet_content($css, TRUE) . "\n/*]]>*/-->\n" . '</style>';
     drupal_add_css($css, array('type' => 'inline', 'preprocess' => TRUE));
     $styles = drupal_get_css();
     $this->assertEqual(trim($styles), $css_preprocessed, t('Rendering preprocessed inline CSS adds it to the page.'));