diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index cebe699..f2cbc9a 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -161,6 +161,48 @@ public function addClass() {
   }
 
   /**
+   * Adds attribute or merges values on to array of existing attribute values.
+   *
+   * @param string $attribute
+   *   Name of the Attribute.
+   * @param string|array $value
+   *   Value(s) to add or merge to the given attribute.
+   *
+   * @return $this
+   */
+  public function setAttribute($attribute, $value) {
+    // If attribute key exists we can set attribute.
+      $this->offsetSet($attribute, $value);
+
+    return $this;
+  }
+
+  /**
+   * Removes argument from array of existing attributes.
+   *
+   * @param string|array ...
+   *   Attributes to remove from the attribute array.
+   *
+   * @return $this
+   */
+  public function removeAttribute() {
+    $args = func_get_args();
+    foreach ($args as $arg) {
+      // Support arrays or multiple arguments.
+      if (is_array($arg)) {
+        foreach ($arg as $value) {
+          unset($this->storage[$value]);
+        }
+      }
+      else {
+        unset($this->storage[$arg]);
+      }
+    }
+
+    return $this;
+  }
+
+  /**
    * Removes argument values from array of existing CSS classes.
    *
    * @param string|array ...
diff --git a/core/lib/Drupal/Core/Template/AttributeBoolean.php b/core/lib/Drupal/Core/Template/AttributeBoolean.php
index 4e9ea67..d3d4a45 100644
--- a/core/lib/Drupal/Core/Template/AttributeBoolean.php
+++ b/core/lib/Drupal/Core/Template/AttributeBoolean.php
@@ -39,6 +39,13 @@ public function render() {
   }
 
   /**
+   * Returns the boolean value.
+   */
+  public function value() {
+    return $this->value;
+  }
+
+  /**
    * Implements the magic __toString() method.
    */
   public function __toString() {