diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 4f1fb61..daf5cac 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -996,8 +996,8 @@ function theme($hook, $variables = array()) {

   // Supply original caller info.
   $variables += array(
-    'theme_hook' => $base_theme_hook,
-    'theme_hook_original' => $original_hook,
+    '#theme_hook' => $base_theme_hook,
+    '#theme_hook_original' => $original_hook,
   );

   // Invoke hook_theme_suggestions_HOOK().
@@ -1054,10 +1054,18 @@ function theme($hook, $variables = array()) {
     $prepare_hooks[] = 'theme_prepare_' . $original_hook;
   }

+  // Send prepare arguments to invoke hooks with $variables passed by reference.
+  $prepare_args = array(&$variables, $base_theme_hook);
+
   // Invokes hook_theme_prepare(), hook_theme_prepare_THEME_HOOK() for enabled
   // modules.
   foreach ($prepare_hooks as $prepare_hook) {
-    $variables = NestedArray::mergeDeep($variables, (array) Drupal::moduleHandler()->invokeAll($prepare_hook, array($variables, $base_theme_hook)));
+    foreach (\Drupal::moduleHandler()->getImplementations($prepare_hook) as $module) {
+      $prepare_function = $module . '_' . $prepare_hook;
+      if (function_exists($prepare_function)) {
+        call_user_func_array($prepare_function, $prepare_args);
+      }
+    }
   }

   // Invokes hook_theme_prepare(), hook_theme_prepare_THEME_HOOK() for the active
@@ -1065,7 +1073,7 @@ function theme($hook, $variables = array()) {
   // @todo Replace with Drupal::themeHandler()->invoke() once implemented.
   // @see https://drupal.org/node/2029819
   foreach ($prepare_hooks as $prepare_hook) {
-    $variables = NestedArray::mergeDeep($variables, (array) theme_invoke($prepare_hook, array($variables, $base_theme_hook)));
+    theme_invoke($prepare_hook, $prepare_args);
   }

   // Invokes hook_preprocess() and hook_preprocess_HOOK() implementations. This
@@ -1577,7 +1585,7 @@ function theme_disable($theme_list) {
  * @param string $hook
  *   The hook name to invoke.
  * @param array $args
- *   The array of arguments to pass to hook invocation.
+ *   The array of arguments to pass to hook invocation (by reference).
  *
  * @return mixed
  *   The value returned varies on which hook is invoked.
@@ -1585,7 +1593,7 @@ function theme_disable($theme_list) {
  * @todo Remove once a proper Drupal::themeHandler() is created.
  * @see https://drupal.org/node/2029819
  */
-function theme_invoke($hook, $args = array()) {
+function theme_invoke($hook, &$args = array()) {
   // Allow the active theme to invoke hooks after the theme system has been
   // initialized.
   global $theme, $base_theme_info;
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemePrepareTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemePrepareTest.php
index 8b1ed5d..089ab48 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemePrepareTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemePrepareTest.php
@@ -36,18 +36,31 @@ function setUp() {

   function testThemePrepare() {
     $this->drupalGet('theme-test/prepare');
-    $this->assertText('Inserted variable1 via hook_theme_prepare().');
-    $this->assertText('Inserted variable2 via hook_theme_prepare_BASE_THEME_ID().');
-    $this->assertText('Inserted themeVariable1 via theme hook_theme_prepare().');
-    $this->assertText('Inserted themeVariable2 via theme hook_theme_prepare_BASE_THEME_ID().');
-  }
-
-  function testThemePrepareAlter() {
-    $this->drupalGet('theme-test/prepare-alter');
-    $this->assertText('Inserted variable1 via hook_theme_prepare() was altered by hook_theme_prepare_alter().');
-    $this->assertText('Inserted variable2 via hook_theme_prepare_BASE_THEME_ID() was altered by hook_theme_prepare_BASE_THEME_ID_alter().');
-    $this->assertText('Inserted themeVariable1 via theme hook_theme_prepare() was altered by theme hook_theme_prepare_alter().');
-    $this->assertText('Inserted themeVariable2 via theme hook_theme_prepare_BASE_THEME_ID() was altered by theme hook_theme_prepare_BASE_THEME_ID_alter().');
+    $this->assertRaw('<p>moduleVariable1: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleVariable2: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleVariableSuggestion1: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleVariableSuggestion2: Drupal\theme_test\ThemeTestController::prepare|theme_test_theme_prepare_theme_test_prepare__implemented|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|test_theme_theme_prepare_theme_test_prepare__implemented|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter|theme_test_theme_prepare_theme_test_prepare__implemented_alter</p>');
+    $this->assertRaw('<p>moduleVariableSuggestion3: Drupal\theme_test\ThemeTestController::prepare|theme_test_theme_prepare_theme_test_prepare__implemented__extended|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|test_theme_theme_prepare_theme_test_prepare__implemented__extended|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter|theme_test_theme_prepare_theme_test_prepare__implemented__extended_alter</p>');
+    $this->assertRaw('<p>moduleElement1: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable1: theme_test_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable2: theme_test_theme_prepare_theme_test_prepare_element|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>themeInjectedVariable1: test_theme_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable3: theme_test_theme_prepare_theme_test_prepare_element_alter|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleElementSuggestion1: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable1: theme_test_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable2: theme_test_theme_prepare_theme_test_prepare_element|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>themeInjectedVariable1: test_theme_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable3: theme_test_theme_prepare_theme_test_prepare_element_alter|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleElementSuggestion2: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable1: theme_test_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable2: theme_test_theme_prepare_theme_test_prepare_element|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>themeInjectedVariable1: test_theme_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable3: theme_test_theme_prepare_theme_test_prepare_element_alter|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleElementSuggestion3: Drupal\theme_test\ThemeTestController::prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable1: theme_test_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable2: theme_test_theme_prepare_theme_test_prepare_element|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>themeInjectedVariable1: test_theme_theme_prepare|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
+    $this->assertRaw('<p>moduleInjectedVariable3: theme_test_theme_prepare_theme_test_prepare_element_alter|test_theme_theme_prepare|test_theme_theme_prepare_theme_test_prepare|theme_test_theme_prepare_alter|test_theme_theme_prepare_alter</p>');
   }

 }
diff --git a/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/ThemeTestController.php b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/ThemeTestController.php
index 1389cea..9becb7d 100644
--- a/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/ThemeTestController.php
+++ b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/ThemeTestController.php
@@ -121,20 +121,67 @@ function functionSuggestionAlter() {
   }

   /**
-   * Menu callback for testing hook_theme_prepare().
+   * Menu callback for testing hook_theme[_THEME_HOOK]_prepare[_alter]().
    */
   function prepare() {
     return array(
-      '#theme' => 'theme_test_prepare_variable',
-    );
-  }
-
-  /**
-   * Menu callback for testing hook_theme_prepare_alter().
-   */
-  function prepareAlter() {
-    return array(
-      '#theme' => 'theme_test_prepare_alter_variable',
+      'moduleVariable1' => array(
+        '#theme' => 'theme_test_prepare',
+        '#title' => 'moduleVariable1',
+        '#value' => __METHOD__,
+      ),
+      'moduleVariable2' => array(
+        '#theme' => 'theme_test_prepare',
+        '#title' => 'moduleVariable2',
+        '#value' => __METHOD__,
+      ),
+      'moduleVariableSuggestion1' => array(
+        '#theme' => 'theme_test_prepare__fallback',
+        '#title' => 'moduleVariableSuggestion1',
+        '#value' => __METHOD__,
+      ),
+      'moduleVariableSuggestion2' => array(
+        '#theme' => 'theme_test_prepare__implemented',
+        '#title' => 'moduleVariableSuggestion2',
+        '#value' => __METHOD__,
+      ),
+      'moduleVariableSuggestion3' => array(
+        '#theme' => 'theme_test_prepare__implemented__extended',
+        '#title' => 'moduleVariableSuggestion3',
+        '#value' => __METHOD__,
+      ),
+      'moduleElement1' => array(
+        '#theme' => 'theme_test_prepare_element',
+        'moduleElement1' => array(
+          '#theme' => 'theme_test_prepare',
+          '#title' => 'moduleElement1',
+          '#value' => __METHOD__,
+        ),
+      ),
+      'moduleElementSuggestion1' => array(
+        '#theme' => 'theme_test_prepare_element__fallback',
+        'moduleElementSuggestion1' => array(
+          '#theme' => 'theme_test_prepare',
+          '#title' => 'moduleElementSuggestion1',
+          '#value' => __METHOD__,
+        ),
+      ),
+      'moduleElementSuggestion2' => array(
+        '#theme' => 'theme_test_prepare_element__implemented',
+        'moduleElementSuggestion2' => array(
+          '#theme' => 'theme_test_prepare',
+          '#title' => 'moduleElementSuggestion2',
+          '#value' => __METHOD__,
+        ),
+      ),
+      'moduleElementSuggestion3' => array(
+        '#theme' => 'theme_test_prepare_element__implemented__extended',
+        'moduleElementSuggestion3' => array(
+          '#theme' => 'theme_test_prepare',
+          '#title' => 'moduleElementSuggestion3',
+          '#value' => __METHOD__,
+        ),
+      ),
     );
   }

diff --git a/core/modules/system/tests/modules/theme_test/theme_test.module b/core/modules/system/tests/modules/theme_test/theme_test.module
index bab08b3..b088e7d 100644
--- a/core/modules/system/tests/modules/theme_test/theme_test.module
+++ b/core/modules/system/tests/modules/theme_test/theme_test.module
@@ -42,11 +42,12 @@ function theme_test_theme($existing, $type, $theme, $path) {
   $items['theme_test_function_template_override'] = array(
     'variables' => array(),
   );
-  $items['theme_test_prepare_variable'] = array(
-    'variables' => array('element' => array()),
+  // hook_theme_prepare() theme hooks.
+  $items['theme_test_prepare'] = array(
+    'variables' => array('hook' => NULL, 'title' => NULL, 'value' => NULL),
   );
-  $items['theme_test_prepare_alter_variable'] = array(
-    'variables' => array('element' => array()),
+  $items['theme_test_prepare_element'] = array(
+    'render element' => 'element',
   );
   return $items;
 }
@@ -84,10 +85,6 @@ function theme_test_menu() {
     'theme callback' => '_theme_custom_theme',
     'route_name' => 'theme_test.prepare',
   );
-  $items['theme-test/prepare-alter'] = array(
-    'theme callback' => '_theme_custom_theme',
-    'route_name' => 'theme_test.prepare_alter',
-  );
   return $items;
 }
 /**
@@ -175,73 +172,100 @@ function theme_theme_test_function_suggestions($variables) {
 }

 /**
- * Implements hook_theme_suggestions_HOOK().
+ * Returns HTML for theme_test_prepare theme hook.
  */
-function theme_test_theme_suggestions_theme_test_suggestion_provided(array $variables) {
-  return array('theme_test_suggestion_provided__' . 'foo');
+function theme_theme_test_prepare($variables) {
+  $title = $variables['title'];
+  $value = $variables['value'];
+  return "<p>$title: $value</p>";
 }

-function theme_theme_test_prepare_variable($variables) {
+/**
+ * Theme function for testing rendering of theme_test_prepare_element().
+ */
+function theme_theme_test_prepare_element($variables) {
   return drupal_render($variables['element']);
 }

-function theme_theme_test_prepare_alter_variable($variables) {
-  return drupal_render($variables['element']);
+/**
+ * Implements hook_theme_suggestions_HOOK().
+ */
+function theme_test_theme_suggestions_theme_test_suggestion_provided(array $variables) {
+  return array('theme_test_suggestion_provided__' . 'foo');
 }

 /**
  * Implements hook_theme_prepare().
  */
-function theme_test_theme_prepare($context) {
-  $variables = array();
-  if ($context['theme_hook'] == 'theme_test_prepare_variable' || $context['theme_hook'] == 'theme_test_prepare_alter_variable') {
-    $variables['element'] = array(
-      'variable1' => array(
-        '#markup' => '<p>Inserted variable1 via hook_theme_prepare().</p>',
-      ),
+function theme_test_theme_prepare(&$variables, $hook) {
+  // Only prepare for the base hook.
+  if ($hook === 'theme_test_prepare') {
+    $variables['hook'] = $variables['#theme_hook_original'];
+  }
+  elseif ($hook === 'theme_test_prepare_element') {
+    $variables['element']['moduleInjectedVariable1'] = array(
+      '#theme' => 'theme_test_prepare__element',
+      '#title' => 'moduleInjectedVariable1',
+      '#value' => __FUNCTION__,
     );
   }
-  return $variables;
 }

 /**
- * Implements hook_theme_prepare_BASE_THEME_ID().
+ * Implements hook_theme_prepare_alter().
  */
-function theme_test_theme_prepare_theme_test_prepare_variable() {
-  $variables = array();
-  $variables['element'] = array(
-    'variable2' => array(
-      '#markup' => '<p>Inserted variable2 via hook_theme_prepare_BASE_THEME_ID().</p>',
-    ),
-  );
-  return $variables;
+function theme_test_theme_prepare_alter(&$variables, $hook) {
+  if ($hook === 'theme_test_prepare') {
+    $variables['value'] .= '|' . __FUNCTION__;
+  }
 }

 /**
- * Implements hook_theme_prepare_BASE_THEME_ID().
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION().
  */
-function theme_test_theme_prepare_theme_test_prepare_alter_variable() {
-  $variables = array();
-  $variables['element'] = array(
-    'variable2' => array(
-      '#markup' => '<p>Inserted variable2 via hook_theme_prepare_BASE_THEME_ID().</p>',
-    ),
-  );
-  return $variables;
+function theme_test_theme_prepare_theme_test_prepare__implemented(&$variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
 }

 /**
- * Implements hook_theme_prepare_alter().
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION_alter().
  */
-function theme_test_theme_prepare_alter(&$variables, $context) {
-  if ($context['theme_hook'] == 'theme_test_prepare_alter_variable') {
-    $variables['element']['variable1']['#markup'] = '<p>Inserted variable1 via hook_theme_prepare() was altered by hook_theme_prepare_alter().</p>';
-  }
+function theme_test_theme_prepare_theme_test_prepare__implemented_alter(&$variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
 }

 /**
- * Implements hook_theme_prepare_BASE_THEME_ID_alter().
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION__SUGGESTION().
  */
-function theme_test_theme_prepare_theme_test_prepare_alter_variable_alter(&$variables) {
-  $variables['element']['variable2']['#markup'] = '<p>Inserted variable2 via hook_theme_prepare_BASE_THEME_ID() was altered by hook_theme_prepare_BASE_THEME_ID_alter().</p>';
+function theme_test_theme_prepare_theme_test_prepare__implemented__extended(&$variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION__SUGGESTION_alter().
+ */
+function theme_test_theme_prepare_theme_test_prepare__implemented__extended_alter(&$variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK().
+ */
+function theme_test_theme_prepare_theme_test_prepare_element(&$variables) {
+  $variables['element']['moduleInjectedVariable2'] = array(
+    '#theme' => 'theme_test_prepare__element',
+    '#title' => 'moduleInjectedVariable2',
+    '#value' => __FUNCTION__,
+  );
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK().
+ */
+function theme_test_theme_prepare_theme_test_prepare_element_alter(&$variables) {
+  $variables['element']['moduleInjectedVariable3'] = array(
+    '#theme' => 'theme_test_prepare__element',
+    '#title' => 'moduleInjectedVariable3',
+    '#value' => __FUNCTION__,
+  );
 }
diff --git a/core/modules/system/tests/modules/theme_test/theme_test.routing.yml b/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
index 53842d4..3c2f46e 100644
--- a/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
+++ b/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
@@ -83,3 +83,10 @@ theme_test.prepare_alter:
     _content: '\Drupal\theme_test\ThemeTestController::prepareAlter'
   requirements:
     _permission: 'access content'
+
+theme_test.prepare_suggestion:
+  path: '/theme-test/prepare-suggestion'
+  defaults:
+    _content: '\Drupal\theme_test\ThemeTestController::prepareSuggestion'
+  requirements:
+    _permission: 'access content'
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.theme b/core/modules/system/tests/themes/test_theme/test_theme.theme
index 2fec7d3..3ed2b73 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.theme
+++ b/core/modules/system/tests/themes/test_theme/test_theme.theme
@@ -73,56 +73,66 @@ function test_theme_theme_test_function_suggestions__module_override($variables)
 /**
  * Implements hook_theme_prepare().
  */
-function test_theme_theme_prepare($context) {
-  $variables = array();
-  if ($context['theme_hook'] == 'theme_test_prepare_variable' || $context['theme_hook'] == 'theme_test_prepare_alter_variable') {
-    $variables['element'] = array(
-      'themeVariable1' => array(
-        '#markup' => '<p>Inserted themeVariable1 via theme hook_theme_prepare().</p>',
-      ),
+function test_theme_theme_prepare(&$variables, $hook) {
+  if ($hook === 'theme_test_prepare') {
+    $variables['value'] .= '|' . __FUNCTION__;
+  }
+  elseif ($hook === 'theme_test_prepare_element') {
+    $variables['element']['themeInjectedVariable1'] = array(
+      '#theme' => 'theme_test_prepare__element',
+      '#title' => 'themeInjectedVariable1',
+      '#value' => __FUNCTION__,
     );
   }
-  return $variables;
 }

 /**
- * Implements hook_theme_prepare_THEME_HOOK().
+ * Implements hook_theme_prepare_alter().
  */
-function test_theme_theme_prepare_theme_test_prepare_variable() {
-  $variables = array();
-  $variables['element'] = array(
-    'themeVariable2' => array(
-      '#markup' => '<p>Inserted themeVariable2 via theme hook_theme_prepare_BASE_THEME_ID().</p>',
-    ),
-  );
-  return $variables;
+function test_theme_theme_prepare_alter(&$variables, $hook) {
+  if ($hook === 'theme_test_prepare') {
+    $variables['value'] .= '|' . __FUNCTION__;
+  }
 }

 /**
  * Implements hook_theme_prepare_THEME_HOOK().
  */
-function test_theme_theme_prepare_theme_test_prepare_alter_variable() {
-  $variables = array();
-  $variables['element'] = array(
-    'themeVariable2' => array(
-      '#markup' => '<p>Inserted themeVariable2 via theme hook_theme_prepare_BASE_THEME_ID().</p>',
-    ),
-  );
-  return $variables;
+function test_theme_theme_prepare_theme_test_prepare(&$variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
 }

 /**
- * Implements hook_theme_prepare_alter().
+ * Implements hook_theme_prepare_THEME_HOOK_alter().
  */
-function test_theme_theme_prepare_alter(&$variables, $context) {
-  if ($context['theme_hook'] == 'theme_test_prepare_alter_variable') {
-    $variables['element']['themeVariable1']['#markup'] = '<p>Inserted themeVariable1 via theme hook_theme_prepare() was altered by theme hook_theme_prepare_alter().</p>';
-  }
+function test_theme_theme_prepare_theme_test_prepare_alter($variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION().
+ */
+function test_theme_theme_prepare_theme_test_prepare__implemented($variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION_alter().
+ */
+function test_theme_theme_prepare_theme_test_prepare__implemented_alter($variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
+}
+
+/**
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION__SUGGESTION().
+ */
+function test_theme_theme_prepare_theme_test_prepare__implemented__extended($variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
 }

 /**
- * Implements hook_theme_prepare_BASE_THEME_ID_alter().
+ * Implements hook_theme_prepare_THEME_HOOK__SUGGESTION__SUGGESTION_alter().
  */
-function test_theme_theme_prepare_theme_test_prepare_alter_variable_alter(&$variables) {
-  $variables['element']['themeVariable2']['#markup'] = '<p>Inserted themeVariable2 via theme hook_theme_prepare_BASE_THEME_ID() was altered by theme hook_theme_prepare_BASE_THEME_ID_alter().</p>';
+function test_theme_theme_prepare_theme_test_prepare__implemented__extended_alter($variables) {
+  $variables['value'] .= '|' . __FUNCTION__;
 }