diff -u b/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
--- b/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -117,6 +117,26 @@
   }
 
   /**
+   * Adds the argument values to the class element.
+   */
+  public function addClass() {
+    $args = func_get_args();
+    foreach ($args as $arg) {
+      $this->storage['class']->add($arg);
+    }
+  }
+
+  /**
+   * Removes the argument values from the class element.
+   */
+  public function removeClass() {
+    $args = func_get_args();
+    foreach ($args as $arg) {
+      $this->storage['class']->remove($arg);
+    }
+  }
+
+  /**
    * Implements the magic __toString() method.
    */
   public function __toString() {
diff -u b/core/lib/Drupal/Core/Template/AttributeArray.php b/core/lib/Drupal/Core/Template/AttributeArray.php
--- b/core/lib/Drupal/Core/Template/AttributeArray.php
+++ b/core/lib/Drupal/Core/Template/AttributeArray.php
@@ -72,18 +72,17 @@
   /**
    * Adds the argument values by merging them on to the value array.
    *
+   * @param string $value
+   *   A value to add to the array.
+   *
    * @return \Drupal\Core\Template\AttributeArray
    *   The attribute array with the arguments added.
    */
-  public function add() {
-    $args = func_get_args();
-    foreach ($args as $arg) {
-      // Merge the values passed in from the value array.
-      // The argument is cast to an array to support comma separated single
-      // values or one or more array arguments.
-      $this->value = array_merge($this->value, (array) $arg);
-    }
-
+  public function add($value) {
+    // Merge the values passed in from the value array.
+    // The argument is cast to an array to support comma separated single
+    // values or one or more array arguments.
+    $this->value = array_merge($this->value, (array) $value);
     // Filter out any empty values.
     $this->value = array_filter($this->value);
     return $this;
@@ -92,18 +91,17 @@
   /**
    * Removes the argument values from the value array.
    *
+   * @param string $value
+   *   A value to remove to the array.
+   *
    * @return \Drupal\Core\Template\AttributeArray
    *   The attribute array with the arguments removed.
    */
-  public function remove() {
-    $args = func_get_args();
-    foreach ($args as $arg) {
-      // Remove the values passed in from the value array.
-      // The argument is cast to an array to support comma separated single
-      // values or one or more array arguments.
-      $this->value = array_diff($this->value, (array) $arg);
-    }
-
+  public function remove($value) {
+    // Remove the values passed in from the value array.
+    // The argument is cast to an array to support comma separated single
+    // values or one or more array arguments.
+    $this->value = array_diff($this->value, (array) $value);
     // Filter out any empty values.
     $this->value = array_filter($this->value);
     return $this;
diff -u b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
--- b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -65,11 +65,11 @@
     $attribute = new Attribute(array('class' => array('example-class')));
 
     // Add one class.
-    $attribute['class']->add('aa');
+    $attribute->addClass('aa');
     $this->assertEquals(new AttributeArray('class', array('example-class', 'aa')), $attribute['class']);
 
     // Add multiple classes.
-    $attribute['class']->add('xx', 'yy');
+    $attribute->addClass('xx', 'yy');
     $this->assertEquals(
       new AttributeArray(
         'class',
@@ -78,7 +78,7 @@
     );
 
     // Add an array of classes.
-    $attribute['class']->add(array('red', 'green', 'blue'));
+    $attribute->addClass(array('red', 'green', 'blue'));
     $this->assertEquals(
       new AttributeArray(
         'class',
@@ -100,15 +100,15 @@
     );
 
     // Remove one class.
-    $attribute['class']->remove('example-class');
+    $attribute->removeClass('example-class');
     $this->assertFalse(in_array('example-class', $attribute['class']->value()));
 
     // Remove multiple classes.
-    $attribute['class']->remove('xx', 'yy');
+    $attribute->removeClass('xx', 'yy');
     $this->assertFalse(in_array(array('xx', 'yy'), $attribute['class']->value()));
 
     // Remove an array of classes.
-    $attribute['class']->remove(array('red', 'green', 'blue'));
+    $attribute->removeClass(array('red', 'green', 'blue'));
     $this->assertFalse(in_array(array('red', 'green', 'blue'), $attribute['class']->value()));
   }