diff --git a/core/lib/Drupal/Core/Config/Schema/ArrayElement.php b/core/lib/Drupal/Core/Config/Schema/ArrayElement.php
index 5dc9893..479c8cf 100644
--- a/core/lib/Drupal/Core/Config/Schema/ArrayElement.php
+++ b/core/lib/Drupal/Core/Config/Schema/ArrayElement.php
@@ -47,10 +47,20 @@ protected function parse() {
   }
 
   /**
+   * Gets data definition object for contained element.
+   *
+   * @param int|string $key
+   *   Property name or index of the element.
+   *
+   * @return \Drupal\Core\TypedData\DataDefinitionInterface
+   */
+  protected abstract function getElementDefinition($key);
+
+  /**
    * {@inheritdoc}
    */
-  public function get($property_name) {
-    $parts = explode('.', $property_name);
+  public function get($name) {
+    $parts = explode('.', $name);
     $root_key = array_shift($parts);
     $elements = $this->getElements();
     if (isset($elements[$root_key])) {
@@ -116,7 +126,7 @@ public function toArray() {
   /**
    * {@inheritdoc}
    */
-  public function onChange($key) {
+  public function onChange($name) {
     // Notify the parent of changes.
     if (isset($this->parent)) {
       $this->parent->onChange($this->name);
@@ -124,13 +134,6 @@ public function onChange($key) {
   }
 
   /**
-   * Implements Countable::count().
-   */
-  public function count() {
-    return count($this->getElements());
-  }
-
-  /**
    * Implements IteratorAggregate::getIterator();
    */
   public function getIterator() {
diff --git a/core/lib/Drupal/Core/Config/Schema/Mapping.php b/core/lib/Drupal/Core/Config/Schema/Mapping.php
index 82f4adc..5adfc20 100644
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
@@ -28,7 +28,7 @@ class Mapping extends ArrayElement {
   /**
    * {@inheritdoc}
    */
-  public function getElementDefinition($key) {
+  protected function getElementDefinition($key) {
     $value = isset($this->value[$key]) ? $this->value[$key] : NULL;
     $definition = isset($this->definition['mapping'][$key]) ? $this->definition['mapping'][$key] : array();
     return $this->buildDataDefinition($definition, $value, $key);
diff --git a/core/lib/Drupal/Core/Config/Schema/Sequence.php b/core/lib/Drupal/Core/Config/Schema/Sequence.php
index 094f5e8..b7c34c2 100644
--- a/core/lib/Drupal/Core/Config/Schema/Sequence.php
+++ b/core/lib/Drupal/Core/Config/Schema/Sequence.php
@@ -21,7 +21,7 @@ class Sequence extends ArrayElement {
   /**
    * {@inheritdoc}
    */
-  public function getElementDefinition($key) {
+  protected function getElementDefinition($key) {
     $value = isset($this->value[$key]) ? $this->value[$key] : NULL;
     $definition = isset($this->definition['sequence'][0]) ? $this->definition['sequence'][0] : array();
     return $this->buildDataDefinition($definition, $value, $key);
diff --git a/core/lib/Drupal/Core/Config/Schema/TypedConfigInterface.php b/core/lib/Drupal/Core/Config/Schema/TypedConfigInterface.php
index 82120b8..8ce63df 100644
--- a/core/lib/Drupal/Core/Config/Schema/TypedConfigInterface.php
+++ b/core/lib/Drupal/Core/Config/Schema/TypedConfigInterface.php
@@ -20,17 +20,16 @@
  * When implementing this interface which extends Traversable, make sure to list
  * IteratorAggregate or Iterator before this interface in the implements clause.
  */
-interface TypedConfigInterface extends TraversableTypedDataInterface, \Countable {
+interface TypedConfigInterface extends TraversableTypedDataInterface {
 
   /**
-   * Determines whether the list contains any non-empty items.
+   * Determines whether the data structure is empty.
    *
    * @return boolean
-   *   TRUE if the list is empty, FALSE otherwise.
+   *   TRUE if the data structure is empty, FALSE otherwise.
    */
   public function isEmpty();
 
-
   /**
    * Gets an array of contained elements.
    *
@@ -39,21 +38,10 @@ public function isEmpty();
    */
   public function getElements();
 
-
-  /**
-   * Gets data definition object for contained element.
-   *
-   * @param int|string $key
-   *   Property name or index of the element.
-   *
-   * @return \Drupal\Core\TypedData\DataDefinitionInterface
-   */
-  public function getElementDefinition($key);
-
   /**
    * Gets a contained typed configuration element.
    *
-   * @param $property_name
+   * @param $name
    *   The name of the property to get; e.g., 'title' or 'name'. Nested
    *   elements can be get using multiple dot delimited names, for example,
    *   'page.front'.
@@ -64,7 +52,7 @@ public function getElementDefinition($key);
    * @return \Drupal\Core\TypedData\TypedDataInterface
    *   The property object.
    */
-  public function get($property_name);
+  public function get($name);
 
   /**
    * Replaces the item at the specified position in this list.
@@ -87,13 +75,4 @@ public function set($key, $value);
    */
   public function toArray();
 
-  /**
-   * React to changes to a child element.
-   *
-   * Note that this is invoked after any changes have been applied.
-   *
-   * @param $key
-   *   The key of the property which is changed.
-   */
-  public function onChange($key);
 }
diff --git a/core/modules/config/src/Tests/ConfigSchemaTest.php b/core/modules/config/src/Tests/ConfigSchemaTest.php
index a23c90d..e8e04f4 100644
--- a/core/modules/config/src/Tests/ConfigSchemaTest.php
+++ b/core/modules/config/src/Tests/ConfigSchemaTest.php
@@ -292,12 +292,10 @@ function testSchemaData() {
     // Now let's try something more complex, with nested objects.
     $wrapper = \Drupal::service('config.typed')->get('image.style.large');
     $effects = $wrapper->get('effects');
-
-    // The function is_array() doesn't work with ArrayAccess, so we use count().
-    $this->assertTrue(count($effects) == 1, 'Got an array with effects for image.style.large data');
+    $this->assertTrue(count($effects->toArray()) == 1, 'Got an array with effects for image.style.large data');
     $uuid = key($effects->getValue());
     $effect = $effects->get($uuid)->getElements();
-    $this->assertTrue(count($effect['data']) && $effect['id']->getValue() == 'image_scale', 'Got data for the image scale effect from metadata.');
+    $this->assertTrue(!$effect['data']->isEmpty() && $effect['id']->getValue() == 'image_scale', 'Got data for the image scale effect from metadata.');
     $this->assertTrue($effect['data']->get('width') instanceof IntegerInterface, 'Got the right type for the scale effect width.');
     $this->assertEqual($effect['data']->get('width')->getValue(), 480, 'Got the right value for the scale effect width.' );