diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index 3ea18b1..ae671d0 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -251,14 +251,18 @@ public function hasClass($class) {
    * Implements the magic __toString() method.
    */
   public function __toString() {
-    $return = '';
+    $keys = '';
+    $values = [];
+    $rendered = FALSE;
     foreach ($this->storage as $name => $value) {
       $rendered = $value->render();
       if ($rendered) {
-        $return .= ' ' . $rendered;
+        $keys .= ' @' . $name;
+        $values['@' . $name] = $rendered;
       }
     }
-    return SafeMarkup::set($return);
+
+    return $keys ? SafeMarkup::format($keys, $values) : '';
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Template/AttributeArray.php b/core/lib/Drupal/Core/Template/AttributeArray.php
index 4cdd932..d7465e8 100644
--- a/core/lib/Drupal/Core/Template/AttributeArray.php
+++ b/core/lib/Drupal/Core/Template/AttributeArray.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\Core\Template;
 
-use Drupal\Component\Utility\SafeMarkup;
-
 /**
  * A class that defines a type of Attribute that can be added to as an array.
  *
@@ -76,7 +74,7 @@ public function offsetExists($offset) {
   public function __toString() {
     // Filter out any empty values before printing.
     $this->value = array_unique(array_filter($this->value));
-    return SafeMarkup::checkPlain(implode(' ', $this->value));
+    return implode(' ', $this->value);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Template/AttributeBoolean.php b/core/lib/Drupal/Core/Template/AttributeBoolean.php
index a2e5c02..2fc4bac 100644
--- a/core/lib/Drupal/Core/Template/AttributeBoolean.php
+++ b/core/lib/Drupal/Core/Template/AttributeBoolean.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\Core\Template;
 
-use Drupal\Component\Utility\SafeMarkup;
-
 /**
  * A class that defines a type of boolean HTML attribute.
  *
@@ -42,7 +40,7 @@ public function render() {
    * Implements the magic __toString() method.
    */
   public function __toString() {
-    return $this->value === FALSE ? '' : SafeMarkup::checkPlain($this->name);
+    return $this->value === FALSE ? '' : $this->name;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Template/AttributeString.php b/core/lib/Drupal/Core/Template/AttributeString.php
index 51b1448..1cc5d6c 100644
--- a/core/lib/Drupal/Core/Template/AttributeString.php
+++ b/core/lib/Drupal/Core/Template/AttributeString.php
@@ -30,7 +30,7 @@ class AttributeString extends AttributeValueBase {
    * Implements the magic __toString() method.
    */
   public function __toString() {
-    return SafeMarkup::checkPlain($this->value);
+    return (string) $this->value;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Template/AttributeValueBase.php b/core/lib/Drupal/Core/Template/AttributeValueBase.php
index 4db6dd8..b1f0898 100644
--- a/core/lib/Drupal/Core/Template/AttributeValueBase.php
+++ b/core/lib/Drupal/Core/Template/AttributeValueBase.php
@@ -57,7 +57,7 @@ public function __construct($name, $value) {
   public function render() {
     $value = (string) $this;
     if (isset($this->value) && static::RENDER_EMPTY_ATTRIBUTE || !empty($value)) {
-      return SafeMarkup::checkPlain($this->name) . '="' . $value . '"';
+      return SafeMarkup::format('@name="@value"', ['@name' => $this->name, '@value' => $value]);
     }
   }