diff -u b/core/lib/Drupal/Core/Render/theme.api.php b/core/lib/Drupal/Core/Render/theme.api.php
--- b/core/lib/Drupal/Core/Render/theme.api.php
+++ b/core/lib/Drupal/Core/Render/theme.api.php
@@ -489,7 +489,8 @@
  * preprocess variables for a specific theme hook, whether implemented as a
  * template or function.
  *
- * For more detailed information, see the 'theme.manager' service.
+ * For more detailed information, see @link themeable Theme system overview
+ * topic @endlink.
  *
  * @param $variables
  *   The variables array (modify in place).
@@ -537,7 +538,8 @@
  * hook. It should only be used if a module needs to override or add to the
  * theme preprocessing for a theme hook it didn't define.
  *
- * For more detailed information, see the 'theme.manager' service.
+ * For more detailed information, see @link themeable Theme system overview
+ * topic @endlink.
  *
  * @param $variables
  *   The variables array (modify in place).
diff -u b/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
--- b/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -49,7 +49,7 @@
    *   - theme path: The effective \Drupal\Core\Theme\ActiveTheme::getPath()
    *      during \Drupal\Core\Theme\ThemeManagerInterface::render(), available
    *      as 'directory' variable in templates. For functions, it should point
-   *      to the respective theme.For templates, it should point to the
+   *      to the respective theme. For templates, it should point to the
    *      directory that contains the template.
    *   - includes: (optional) An array of include files to load when the theme
    *     hook is executed by \Drupal\Core\Theme\ThemeManagerInterface::render().
@@ -531,7 +531,7 @@
           }
           foreach ($prefixes as $prefix) {
             // Only use non-hook-specific variable preprocessors for theming
-            // hooks implemented as templates. See the 'theme.manager' service.
+            // hooks implemented as templates. See the @defgroup themeable topic.
             if (isset($info['template']) && function_exists($prefix . '_preprocess')) {
               $info['preprocess functions'][] = $prefix . '_preprocess';
             }
@@ -567,7 +567,7 @@
             $cache[$hook]['preprocess functions'] = array();
           }
           // Only use non-hook-specific variable preprocessors for theme hooks
-          // implemented as templates. See the 'theme.manager' service.
+          // implemented as templates. See the @defgroup themeable topic.
           if (isset($info['template']) && function_exists($name . '_preprocess')) {
             $cache[$hook]['preprocess functions'][] = $name . '_preprocess';
           }
diff -u b/core/lib/Drupal/Core/Theme/ThemeManager.php b/core/lib/Drupal/Core/Theme/ThemeManager.php
--- b/core/lib/Drupal/Core/Theme/ThemeManager.php
+++ b/core/lib/Drupal/Core/Theme/ThemeManager.php
@@ -142,7 +142,7 @@
     // full theme registry to work with, and therefore cannot process the theme
     // request properly. See also \Drupal\Core\Theme\Registry::get().
     if (!$this->moduleHandler->isLoaded() && !defined('MAINTENANCE_MODE')) {
-      throw new \Exception('The theme implementations may not be rendered until all modules are loaded.');
+      throw new \Exception(t('_theme() may not be called until all modules are loaded.'));
     }
 
     $theme_registry = $this->themeRegistry->getRuntime();
diff -u b/core/lib/Drupal/Core/Utility/ThemeRegistry.php b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
--- b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
+++ b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
@@ -26,7 +26,7 @@
   /**
    * Whether the partial registry can be persisted to the cache.
    *
-   * This is only allowed if all modules and the request method is GET.
+   * This is only allowed if the request method is GET.
    * \Drupal\Core\Theme\ThemeManagerInterface::render() should be very rarely
    * called on POST requests and this avoids polluting the runtime cache.
    */
diff -u b/core/modules/image/image.module b/core/modules/image/image.module
--- b/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -103,8 +103,8 @@
       // 'image_style' to pass a meaningful value for the alt variable.
       // - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
       // - http://www.w3.org/TR/xhtml1/dtds.html
-      // - http://dev.w3.org/html5/spec/Overview.html#alt The title attribute is
-      //   optional in all cases, so it is omitted by default.
+      // - http://dev.w3.org/html5/spec/Overview.html#alt 
+      // The title attribute is optional in all cases, so it is omitted by default.
       'variables' => array(
         'style_name' => NULL,
         'uri' => NULL,