diff --git a/core/modules/system/src/Tests/Common/RenderElementTypesTest.php b/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
index e60bb52..4e7226d 100644
--- a/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
+++ b/core/modules/system/src/Tests/Common/RenderElementTypesTest.php
@@ -56,7 +56,7 @@ function testContainer() {
     $this->assertElements(array(
       '#type' => 'container',
       '#markup' => 'foo',
-    ), "<div>foo</div>\n", "#type 'container' with no HTML attributes");
+    ), "<div>\nfoo\n</div>\n", "#type 'container' with no HTML attributes");
 
     // Container with a class.
     $this->assertElements(array(
@@ -65,7 +65,7 @@ function testContainer() {
       '#attributes' => array(
         'class' => array('bar'),
       ),
-    ), '<div class="bar">foo</div>' . "\n", "#type 'container' with a class HTML attribute");
+    ), '<div class="bar">' . "\n" . 'foo' . "\n" . '</div>' . "\n", "#type 'container' with a class HTML attribute");
 
     // Container with children.
     $this->assertElements(array(
@@ -73,7 +73,7 @@ function testContainer() {
       'child' => array(
         '#markup' => 'foo',
       ),
-    ), "<div>foo</div>\n", "#type 'container' with child elements");
+    ), "<div>\nfoo\n</div>\n", "#type 'container' with child elements");
   }
 
   /**
diff --git a/core/modules/system/tests/modules/form_test/src/interdiff-2560467-9-10.txt b/core/modules/system/tests/modules/form_test/src/interdiff-2560467-9-10.txt
new file mode 100644
index 0000000..484aeaa
--- /dev/null
+++ b/core/modules/system/tests/modules/form_test/src/interdiff-2560467-9-10.txt
@@ -0,0 +1,133 @@
+diff --git a/core/includes/theme.inc.rej b/core/includes/theme.inc.rej
+deleted file mode 100644
+index a2c1811..0000000
+--- a/core/includes/theme.inc.rej
++++ /dev/null
+@@ -1,14 +0,0 @@
+-diff a/core/includes/theme.inc b/core/includes/theme.inc	(rejected hunks)
+-@@ -1146,6 +1146,12 @@ function template_preprocess_container(&$variables) {
+- 
+-   $variables['children'] = $element['#children'];
+-   $variables['attributes'] = $element['#attributes'];
+-+
+-+  // Display any error messages.
+-+  $variables['errors'] = NULL;
+-+  if (!empty($element['#errors']) && empty($element['#error_no_message'])) {
+-+   $variables['errors'] = $element['#errors'];
+-+  }
+- }
+- 
+- /**
+diff --git a/core/modules/system/src/Tests/Form/ElementTest.php b/core/modules/system/src/Tests/Form/ElementTest.php
+index 684e13a..0ff443f 100644
+--- a/core/modules/system/src/Tests/Form/ElementTest.php
++++ b/core/modules/system/src/Tests/Form/ElementTest.php
+@@ -162,11 +162,18 @@ public function testFormAutocomplete() {
+   }
+ 
+   /**
+-   * Tests form element error messages.
++   * Tests form details element error messages.
+    */
+-  public function testFormElementErrors() {
++  public function testFormDetailsErrors() {
+     $this->drupalPostForm('form_test/details-form', [], 'Submit');
+     $this->assertText('I am an error on the details element.');
+   }
++  /**
++   * Tests form container element error messages.
++   */
++  public function testFormElementErrors() {
++    $this->drupalPostForm('form_test/container-form', [], 'Submit');
++    $this->assertText('I am an error on the container element.');
++  }
+ 
+ }
+diff --git a/core/modules/system/templates/container.html.twig.rej b/core/modules/system/templates/container.html.twig.rej
+deleted file mode 100644
+index 9f64af5..0000000
+--- a/core/modules/system/templates/container.html.twig.rej
++++ /dev/null
+@@ -1,22 +0,0 @@
+-diff a/core/modules/system/templates/container.html.twig b/core/modules/system/templates/container.html.twig	(rejected hunks)
+-@@ -12,6 +12,7 @@
+-  *
+-  * Available variables:
+-  * - attributes: HTML attributes for the containing element.
+-+ * - errors: (optional) Any errors for this container element, may not be set.
+-  * - children: The rendered child elements of the container.
+-  * - has_parent: A flag to indicate that the container has one or more parent
+-      containers.
+-@@ -27,4 +28,11 @@
+-     has_parent ? 'form-wrapper',
+-   ]
+- %}
+--<div{{ attributes.addClass(classes) }}>{{ children }}</div>
+-+<div{{ attributes.addClass(classes) }}>
+-+{% if errors %}
+-+  <div>
+-+    {{ errors }}
+-+  </div>
+-+{% endif %}
+-+{{ children }}
+-+</div>
+diff --git a/core/modules/system/tests/modules/form_test/form_test.routing.yml b/core/modules/system/tests/modules/form_test/form_test.routing.yml
+index 42a6ba4..327d7fd 100644
+--- a/core/modules/system/tests/modules/form_test/form_test.routing.yml
++++ b/core/modules/system/tests/modules/form_test/form_test.routing.yml
+@@ -409,6 +409,14 @@ form_test.details_form:
+   requirements:
+     _access: 'TRUE'
+ 
++form_test.container_form:
++  path: '/form_test/container-form'
++  defaults:
++    _form: '\Drupal\form_test\Form\FormTestContainerForm'
++    _title: 'Form contaner form test'
++  requirements:
++    _access: 'TRUE'
++
+ form_test.description_display:
+   path: '/form_test/form-descriptions'
+   defaults:
+diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
+index 5949679..55fcbfd 100644
+--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
++++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
+@@ -6,7 +6,7 @@
+ use Drupal\Core\Form\FormStateInterface;
+ 
+ /**
+- * Builds a simple form to test the #group property on #type 'container'.
++ * Builds a simple form to test the #group property on #type 'details'.
+  */
+ class FormTestDetailsForm extends FormBase {
+ 
+diff --git a/core/themes/classy/templates/form/container.html.twig.rej b/core/themes/classy/templates/form/container.html.twig.rej
+deleted file mode 100644
+index db1ca62..0000000
+--- a/core/themes/classy/templates/form/container.html.twig.rej
++++ /dev/null
+@@ -1,22 +0,0 @@
+-diff a/core/themes/classy/templates/form/container.html.twig b/core/themes/classy/templates/form/container.html.twig	(rejected hunks)
+-@@ -12,6 +12,7 @@
+-  *
+-  * Available variables:
+-  * - attributes: HTML attributes for the containing element.
+-+ * - errors: (optional) Any errors for this container element, may not be set.
+-  * - children: The rendered child elements of the container.
+-  * - has_parent: A flag to indicate that the container has one or more parent
+-      containers.
+-@@ -25,4 +26,11 @@
+-     has_parent ? 'form-wrapper',
+-   ]
+- %}
+--<div{{ attributes.addClass(classes) }}>{{ children }}</div>
+-+<div{{ attributes.addClass(classes) }}>
+-+{% if errors %}
+-+  <div class="form-item--error-message">
+-+    <strong>{{ errors }}</strong>
+-+  </div>
+-+{% endif %}
+-+{{ children }}
+-+</div>