diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index d7dae0e..5333acb 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -161,6 +161,47 @@ public function addClass() {
   }
 
   /**
+   * Sets values for an attribute key.
+   *
+   * @param string $attribute
+   *   Name of the attribute.
+   * @param string|array $value
+   *   Value(s) to set for the given attribute key.
+   *
+   * @return $this
+   */
+  public function setAttribute($attribute, $value) {
+    $this->offsetSet($attribute, $value);
+
+    return $this;
+  }
+
+  /**
+   * Removes an attribute from an Attribute object.
+   *
+   * @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/AttributeArray.php b/core/lib/Drupal/Core/Template/AttributeArray.php
index 61c968f..190c898 100644
--- a/core/lib/Drupal/Core/Template/AttributeArray.php
+++ b/core/lib/Drupal/Core/Template/AttributeArray.php
@@ -87,13 +87,6 @@ public function getIterator() {
   }
 
   /**
-   * Returns the whole array.
-   */
-  public function value() {
-    return $this->value;
-  }
-
-  /**
    * Exchange the array for another one.
    *
    * @see ArrayObject::exchangeArray
diff --git a/core/lib/Drupal/Core/Template/AttributeValueBase.php b/core/lib/Drupal/Core/Template/AttributeValueBase.php
index 197b199..ed4dfc3 100644
--- a/core/lib/Drupal/Core/Template/AttributeValueBase.php
+++ b/core/lib/Drupal/Core/Template/AttributeValueBase.php
@@ -62,6 +62,13 @@ public function render() {
   }
 
   /**
+   * Returns the raw value.
+   */
+  public function value() {
+    return $this->value;
+  }
+
+  /**
    * Implements the magic __toString() method.
    */
   abstract function __toString();
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
index 0384da8..fcf8601 100644
--- a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -58,6 +58,79 @@ public function testRemove() {
   }
 
   /**
+   * Tests setting attributes.
+   * @covers ::setAttribute()
+   */
+  public function testSetAttribute() {
+    $attribute = new Attribute();
+
+    // Test adding various attributes.
+    $attributes = ['alt', 'id', 'src', 'title', 'value'];
+    foreach ($attributes as $key) {
+      foreach (['kitten', ''] as $value) {
+        $attribute = new Attribute();
+        $attribute->setAttribute($key, $value);
+        $this->assertEquals($value, $attribute[$key]);
+      }
+    }
+
+    // Test adding array to class.
+    $attribute = new Attribute();
+    $attribute->setAttribute('class', ['kitten', 'cat']);
+    $this->assertArrayEquals(['kitten', 'cat'], $attribute['class']->value());
+
+    // Test adding boolean attributes.
+    $attribute = new Attribute();
+    $attribute['checked'] = TRUE;
+    $this->assertTrue($attribute['checked']->value());
+
+    // Test adding boolean attributes through the constructor.
+    $attribute = new Attribute(['selected' => TRUE, 'checked' => FALSE]);
+    $this->assertTrue($attribute['selected']->value());
+    $this->assertFalse($attribute['checked']->value());
+  }
+
+  /**
+   * Tests removing attributes.
+   * @covers ::removeAttribute()
+   */
+  public function testRemoveAttribute() {
+    $attributes = [
+      'alt' => 'Alternative text',
+      'id' => 'bunny',
+      'src' => 'zebra',
+      'style' => 'color: pink;',
+      'title' => 'kitten',
+      'value' => 'ostrich',
+    ];
+    $attribute = new Attribute($attributes);
+
+    // Single value.
+    $attribute->removeAttribute('alt');
+    $this->assertEmpty($attribute['alt']);
+
+    // Multiple values.
+    $attribute->removeAttribute('id', 'src');
+    $this->assertEmpty($attribute['id']);
+    $this->assertEmpty($attribute['src']);
+
+    // Single value in array.
+    $attribute->removeAttribute(['style']);
+    $this->assertEmpty($attribute['style']);
+
+    // Multiple values in array.
+    $attribute->removeAttribute(['title', 'value']);
+    $this->assertEmpty((string) $attribute);
+
+    // Boolean value.
+    $attribute = new Attribute();
+    $attribute->setAttribute('checked', TRUE);
+    $this->assertTrue($attribute['checked']->value());
+    $attribute->removeAttribute('checked');
+    $this->assertEmpty($attribute['checked']);
+  }
+
+  /**
    * Tests adding class attributes with the AttributeArray helper method.
    * @covers ::addClass()
    */