diff --git a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
index c50e320..7ef8722 100644
--- a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
+++ b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
@@ -12,6 +12,7 @@
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Render\BubbleableMetadata;
+use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\SafeMarkup;
 use Symfony\Component\HttpFoundation\RequestStack;
 
@@ -40,7 +41,6 @@ class HtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorIn
    * Provided so that we can support drupal_processed_attached() as an API.
    *
    * @var array
-   * @todo Remove this in Drupal 9.
    */
   public static $legacyAttached;
 
@@ -411,8 +411,7 @@ protected function processHtmlHeadLink(array $html_head_link) {
 
       if ($should_add_header) {
         // Also add a HTTP header "Link:".
-        // @todo: Change this to Html::escape() after https://www.drupal.org/node/2550945
-        $href = '<' . SafeMarkup::checkPlain($attributes['href']) . '>;';
+        $href = '<' . Html::escape($attributes['href'] . '>');
         unset($attributes['href']);
         $attached['http_header'][] = ['Link', $href . drupal_http_header_attributes($attributes), TRUE];
       }
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 47eac67..cd1e580 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -468,9 +468,6 @@ function template_preprocess_book_export_html(&$variables) {
   $variables['base_url'] = $base_url;
   $variables['language'] = $language_interface;
   $variables['language_rtl'] = ($language_interface->getDirection() == LanguageInterface::DIRECTION_RTL);
-  // @todo: Commenting out the following line is wrong.
-  // @see https://www.drupal.org/node/1338858
-  // $variables['head'] = drupal_get_html_head();
 
   // HTML element attributes.
   $attributes = array();
diff --git a/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php b/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
index 3571efb..02497fb 100644
--- a/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
+++ b/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
@@ -47,13 +47,21 @@ public function testAttachments() {
     $this->assertHeader('X-Drupal-Cache', 'HIT');
 
     // Test ['#attached']['feed'].
-    // @todo: Improve this test.
     $this->drupalGet('/render_attached_test/feed');
-    $this->assertEqual(1, count($this->xpath('//head/link[@rel="alternate"]')), 'Link has rel="alternate"');
-    $this->assertEqual(1, count($this->xpath('//head/link[@type="application/rss+xml"]')), 'Link has proper content type.');
-    $this->assertEqual(1, count($this->xpath('//head/link[@href="test://url"]')), 'Link has URL.');
-    $this->assertEqual(1, count($this->xpath('//head/link[@title=""]')), 'Link has title.');
-    $this->assertHeader('X-Drupal-Cache', 'MISS');
+    // Discover the DOM element for the feed link.
+    $link = $this->xpath('//head/link[@href="test://url"]');
+    $this->assertEqual(1, count($link), 'Link has URL.');
+    // Reconcile the other attributes.
+    $link_attributes = [
+      'href' => 'test://url',
+      'rel' => 'alternate',
+      'type' => 'application/rss+xml',
+      'title' => '',
+     ];
+    $link = reset($link);
+    foreach ($link->attributes() as $attribute => $value) {
+      $this->assertEqual($value, $link_attributes[$attribute]);
+    }
     // Repeat for the cache.
     $this->drupalGet('/render_attached_test/feed');
     $this->assertHeader('X-Drupal-Cache', 'HIT');
@@ -79,13 +87,15 @@ public function testAttachments() {
     $this->assertHeader('X-Drupal-Cache', 'HIT');
 
     // Test ['#attached']['feed'].
-    // @todo: Improve this test.
     $this->drupalGet('/render_attached_test/feed_dpa');
-    $this->assertEqual(1, count($this->xpath('//head/link[@rel="alternate"]')), 'Link has rel="alternate"');
-    $this->assertEqual(1, count($this->xpath('//head/link[@type="application/rss+xml"]')), 'Link has proper content type.');
-    $this->assertEqual(1, count($this->xpath('//head/link[@href="test://url"]')), 'Link has URL.');
-    $this->assertEqual(1, count($this->xpath('//head/link[@title=""]')), 'Link has title.');
-    $this->assertHeader('X-Drupal-Cache', 'MISS');
+    // Discover the DOM element for the feed link.
+    $link = $this->xpath('//head/link[@href="test://url"]');
+    $this->assertEqual(1, count($link), 'Link has URL.');
+    // Reconcile the other attributes.
+    $link = reset($link);
+    foreach ($link->attributes() as $attribute => $value) {
+      $this->assertEqual($value, $link_attributes[$attribute]);
+    }
     // Repeat for the cache.
     $this->drupalGet('/render_attached_test/feed_dpa');
     $this->assertHeader('X-Drupal-Cache', 'HIT');