diff --git a/core/lib/Drupal/Core/Config/Metadata/ConfigElement.php b/core/lib/Drupal/Core/Config/Metadata/ConfigElement.php
new file mode 100644
index 0000000..4f49415
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/Metadata/ConfigElement.php
@@ -0,0 +1,108 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\Core\Config\Metadata\ConfigElement.
+ */
+
+namespace Drupal\Core\Config\Metadata;
+
+use Drupal\Core\Language\Language;
+use Drupal\Core\TypedData\ComplexDataInterface;
+use InvalidArgumentException;
+
+/**
+ * Defines a generic 'configuration element' data type.
+ *
+ * Wraps configuration data and metadata allowing access to configuration data
+ * using the ComplexDataInterface API. This object may contain any number and
+ * type of nested properties.
+ */
+class ConfigElement extends ElementBase implements ComplexDataInterface {
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::get().
+   */
+  public function get($property_name) {
+    if ($property = $this->getElement($property_name)) {
+      return $property;
+    }
+    else {
+      throw new InvalidArgumentException(format_string("The configuration property @key doesn't exist.", array(
+          '@key' => $property_name,
+      )));
+    }
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::set().
+   */
+  public function set($property_name, $value) {
+    // Set the data into the configuration array but behave according to the
+    // interface specification when we've got a null value.
+    if (isset($value)) {
+      $this->value[$property_name] = $value;
+      return $this->get($property_name);
+    }
+    else {
+      // In these objects, when clearing the value, the property is gone.
+      // As this needs to return a property, we get it before we delete it.
+      $property = $this->get($property_name);
+      unset($this->value[$property_name]);
+      $property->setValue($value);
+      return $property;
+    }
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::getProperties().
+   */
+  public function getProperties($include_computed = FALSE) {
+    return $this->toArray();
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyValues().
+   */
+  public function getPropertyValues() {
+    return $this->value;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::setPropertyValues().
+   */
+  public function setPropertyValues($values) {
+    foreach ($values as $name => $value) {
+      $this->value[$name] = $value;
+    }
+    return $this;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinition().
+   */
+  public function getPropertyDefinition($name) {
+    $value = isset($this->value[$name]) ? $this->value[$name] : NULL;
+    $metadata = $this->getElementMetadata($key);
+    $definition = Metadata::buildDefinition($value, $metadata);
+    return $definition ? $definition : FALSE;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinitions().
+   */
+  public function getPropertyDefinitions() {
+    $list = array();
+    foreach ($this->getAllKeys() as $key) {
+      $list[$key] = $this->getPropertyDefinition($key);
+    }
+    return $list;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ComplexDataInterface::isEmpty().
+   */
+  public function isEmpty() {
+    return empty($this->value);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Config/Metadata/ConfigWrapper.php b/core/lib/Drupal/Core/Config/Metadata/ConfigWrapper.php
index 21e9cf2..6d19458 100644
--- a/core/lib/Drupal/Core/Config/Metadata/ConfigWrapper.php
+++ b/core/lib/Drupal/Core/Config/Metadata/ConfigWrapper.php
@@ -7,9 +7,10 @@
 
 namespace Drupal\Core\Config\Metadata;
 
+use Drupal\Core\Config\Config;
 use Drupal\Core\Language\Language;
 use Drupal\Core\TypedData\ComplexDataInterface;
-use InvalidArgumentException;
+use Drupal\Core\TypedData\ListInterface;
 
 /**
  * Defines the configuration wrapper object.
@@ -17,14 +18,14 @@
  * This object wraps the full configuration object's data and is the outermost
  * level for configuration wrappers. All of the others are nested in this one.
  */
-class ConfigWrapper extends WrapperBase implements ComplexDataInterface  {
+class ConfigWrapper extends Config {
 
   /**
-   * The name of the configuration object.
+   * The base typed data element for this configuration data.
    *
-   * @var string
+   * @var Drupal\Core\TypedData\TypedDataInterface
    */
-  protected $name;
+  protected $base;
 
   /**
    * Constructs a configuration wrapper object.
@@ -40,118 +41,101 @@ public function __construct($name, $data) {
   }
 
   /**
-   * Gets the configuration language.
+   * Gets data from this config object.
    *
-   * @return Drupal\Core\Language\Language
-   *   The language object.
-   */
-  public function getLanguage() {
-    $meta = $this->getMetadata();
-    // The default language will be English as this is hardcoded information.
-    $langcode = isset($meta['language']) ? $meta['language'] : 'en';
-    return new Language(array('langcode' => $langcode));
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getKey().
+   * @return mixed
+   *   The data that was requested.
    */
-  public function getKey() {
-    // This is the parent wrapper, so there is no key.
-    return '';
+  public function getData() {
+    return $this->data;
   }
 
   /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getMetadata().
+   * Overrides Drupal\Core\Config\Config::setData().
    */
-  public function getMetadata() {
-    return config_metadata($this->name);
+  public function setData(array $data) {
+    $this->data = $data;
+    $this->setBase();
+    return $this;
   }
 
   /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getBase().
+   * Gets data from this config object as typed data.
+   *
+   * @param string $key
+   *   A string that maps to a key within the configuration data.
+   *
+   * @return Drupal\Core\TypedData\TypedDataInterface
+   *   The data that was requested.
    */
-  public function getBase() {
-    return $this->buildDefinition($this->data, $this->getMetadata());
-  }
+  public function get($key = '') {
+    $element = $this->getBase();
+    if (!empty($key)) {
+      // Get nested element recursively.
+      $parts = explode('.', $key);
+      while ($element && $name = array_shift($parts)) {
+        if ($element instanceof ListInterface) {
+          $element = $element[$name];
+        }
+        elseif ($element instanceof ComplexDataInterface) {
+          $element = $element->get($name);
+        }
+        else {
+          $element = NULL;
+        }
+      }
 
-  /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::get().
-   */
-  public function get($property_name) {
-    if ($property = $this->getElement($property_name)) {
-      return $property;
-    }
-    else {
-      throw new InvalidArgumentException(format_string("The configuration property @key doesn't exist.", array(
-          '@key' => $property_name,
-      )));
     }
+    return $element;
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::set().
+   * Overrides Drupal\Core\Config\Config::set().
    */
-  public function set($property_name, $value) {
-    // Set the data into the configuration array but behave according to the
-    // interface specification when we've got a null value.
-    if (isset($value)) {
-      $this->setElementData($property_name, $value);
-      return $this->get($property_name);
-    }
-    else {
-      // In these objects, when clearing the value, the property is gone.
-      // As this needs to return a property, we get it before we delete it.
-      $property = $this->get($property_name);
-      $this->clearElementData($property_name);
-      $property->setValue($value);
-      return $property;
-    }
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::getProperties().
-   */
-  public function getProperties($include_computed = FALSE) {
-    return $this->toArray();
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyValues().
-   */
-  public function getPropertyValues() {
-    return $this->getData();
+  public function set($key, $value) {
+    parent::set($key, $value);
+    $this->setBase();
+    return $this;
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::setPropertyValues().
+   * Overrides Drupal\Core\Config\Config::clear().
    */
-  public function setPropertyValues($values) {
-    foreach ($values as $name => $value) {
-      $this->set($name, $value);
-    }
+  public function clear($key) {
+    parent::clear($key);
+    $this->setBase();
     return $this;
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinition().
+   * Gets the configuration language.
+   *
+   * @return Drupal\Core\Language\Language
+   *   The language object.
    */
-  public function getPropertyDefinition($name) {
-    $definition = $this->getElementDefinition($name);
-    return $definition ? $definition : FALSE;
+  public function getLanguage() {
+    // The default language will be English as this is hardcoded information.
+    $langcode = isset($this->data['language']) ? $this->data['language'] : 'en';
+    return new Language(array('langcode' => $langcode));
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinitions().
+   * Gets the base configuration element.
    */
-  public function getPropertyDefinitions() {
-    return $this->getChildrenMetadata($this->getMetadata());
+  protected function getBase() {
+    if (!isset($this->base)) {
+      $this->base = Metadata::buildElement($this->data, config_metadata($this->name), '');
+    }
+    return $this->base;
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::isEmpty().
+   * Resets the base element's data.
    */
-  public function isEmpty() {
-    return empty($this->data);
+  protected function setBase() {
+    if (isset($this->base)) {
+      $this->base->setValue($this->data);
+    }
   }
 
 }
diff --git a/core/lib/Drupal/Core/Config/Metadata/ElementBase.php b/core/lib/Drupal/Core/Config/Metadata/ElementBase.php
new file mode 100644
index 0000000..9fcdd7c
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/Metadata/ElementBase.php
@@ -0,0 +1,259 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\Core\Config\Metadata\ElementBase.
+ */
+
+namespace Drupal\Core\Config\Metadata;
+
+use Drupal\Core\Language\Language;
+use Drupal\Core\TypedData\TypedDataInterface;
+use Drupal\Core\TypedData\Type\TypedData;
+use ArrayIterator;
+use IteratorAggregate;
+
+/**
+ * Defines a 'configuration wrapper element' data type.
+ *
+ * Wraps configuration data and metadata allowing access to configuration data
+ * using the TypedDataInterface API. These objects may be nested.
+ *
+ * Supported settings (below the definition's 'settings' key) are:
+ * - 'label', Name of the configuration data property to be used as
+ *   the label for the element definition.
+ */
+abstract class ElementBase extends TypedData implements IteratorAggregate, ElementInterface {
+
+  /**
+   * The configuration key relative to the parent's.
+   *
+   * @var string
+   */
+  protected $key;
+
+  /**
+   * The configuration data.
+   *
+   * @var array
+   */
+  protected $value;
+
+  /**
+   * Full metadata for the element.
+   *
+   * @var array
+   */
+  protected $metadata;
+
+  /**
+   * Parent configuration wrapper.
+   *
+   * @var Drupal\Core\Config\ElementInterface
+   */
+  protected $parent;
+
+  /**
+   * Gets contained typed data object.
+   *
+   * @param string $key
+   *   Configuration key.
+   *
+   * @return \Drupal\Core\TypedData\TypedDataInterface|null
+   *   The property object or null if the property doesn't exist.
+   */
+  protected function getElement($key) {
+    // Only attempt to build the element if it actually has configuration data.
+    if (isset($this->value[$key])) {
+      return Metadata::buildElement($this->value[$key], $this->getElementMetadata($key), $key, $this);
+    }
+    else {
+      return NULL;
+    }
+  }
+
+  /**
+   * Gets the built metadata array for a child element.
+   *
+   * @param $key
+   *   Key from the configuration data array.
+   *
+   * @return array
+   *   The metadata for the element, defaults to an empty array.
+   */
+  protected function getElementMetadata($key) {
+    // Metadata for nested elements must be built before.
+    if (!isset($this->metadata[$key])) {
+      $this->metadata[$key] = $this->buildElementMetadata($key, $this->value[$key]);
+    }
+    return $this->metadata[$key];
+  }
+
+  /**
+   * Builds metadata for a child element.
+   *
+   * @param string $key
+   *   Element's key.
+   * @param mixed $data
+   *   Configuration data for the element.
+   *
+   * @return array
+   *   Configuration metadata for the element.
+   */
+  protected function buildElementMetadata($key, $data) {
+    $metadata = $this->getMetadata();
+    return isset($metadata[$key]) ? $metadata[$key] : array();
+  }
+
+  /**
+   * Gets valid configuration data keys.
+   *
+   * @return array
+   *   Array of valid configuration data keys.
+   */
+  protected function getAllKeys() {
+    return is_array($this->value) ? array_keys($this->value) : array();
+  }
+
+  /**
+   * Gets typed data properties as array.
+   *
+   * @return array
+   *   List of TypedDataInterface objects indexed by key.
+   */
+  protected function toArray() {
+    $array = array();
+    foreach ($this->getAllKeys() as $key) {
+      $array[$key] = $this->getElement($key);
+    }
+    return array_filter($array);
+  }
+
+  /**
+   * Implements Drupal\Core\Config\Metadata\ElementInterface::getKey().
+   */
+  public function getKey() {
+    $parent = isset($this->parent) ? $this->parent->getKey() : NULL;
+    return $parent || is_numeric($parent) ? $parent . '.' . $this->key : $this->key;
+  }
+
+  /**
+   * Implements Drupal\Core\Config\Metadata\ElementInterface::getLabel().
+   */
+  public function getLabel() {
+    return isset($this->definition['label']) ? $this->definition['label'] : $this->getKey();
+  }
+
+  /**
+   * Implements Drupal\Core\Config\Metadata\ElementInterface::toList().
+   */
+  public function toList() {
+    $list = array();
+    foreach ($this->toArray() as $key => $element) {
+      if ($element instanceof ElementInterface) {
+        foreach ($element->toList() as $subkey => $element) {
+          $list[$key . '.' . $subkey] = $element;
+        }
+      }
+      else {
+        $list[$key] = $element;
+      }
+    }
+    return $list;
+  }
+
+  /**
+   * Implements Drupal\Core\Config\Metadata\ElementInterface::getMetadata().
+   */
+  public function getMetadata() {
+    return $this->metadata;
+  }
+
+  /**
+   * Implements Drupal\Core\Config\Metadata\ElementInterface::setMetadata().
+   */
+  public function setMetadata($metadata) {
+    $this->metadata = $metadata;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\TypedDataInterface::validate().
+   */
+  public function validate() {
+    // This will be ok if we have any config data at all.
+    return isset($this->value);
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ContextAwareInterface::getName().
+   */
+  public function getName() {
+    return $this->key;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ContextAwareInterface::setName().
+   */
+  public function setName($name) {
+    $this->key = $name;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ContextAwareInterface::getParent().
+  */
+  public function getParent() {
+    return $this->parent;
+  }
+
+  /**
+   * Implements Drupal\Core\TypedData\ContextAwareInterface::setParent().
+  */
+  public function setParent($parent) {
+    $this->parent = $parent;
+  }
+
+  /**
+   * Implements ArrayAccess::offsetExists().
+   */
+  public function offsetExists($offset) {
+    return isset($this->value[$offset]);
+  }
+
+  /**
+   * Implements ArrayAccess::offsetGet().
+   */
+  public function offsetGet($offset) {
+    return $this->getElement($offset);
+  }
+
+  /**
+   * Implements ArrayAccess::offsetSet().
+   */
+  public function offsetSet($offset, $value) {
+    if ($value instanceof TypedDataInterface) {
+      $value = $value->getValue();
+    }
+    $this->value[$offset] = $value;
+  }
+
+  /**
+   * Implements ArrayAccess::offsetUnset().
+   */
+  public function offsetUnset($offset) {
+    unset($this->value[$offset]);
+  }
+
+  /**
+   * Implements Countable::count().
+   */
+  public function count() {
+    return count($this->getValue());
+  }
+
+  /**
+   * Implements IteratorAggregate::getIterator().
+   */
+  public function getIterator() {
+    return new ArrayIterator($this->toArray());
+  }
+}
diff --git a/core/lib/Drupal/Core/Config/Metadata/ElementInterface.php b/core/lib/Drupal/Core/Config/Metadata/ElementInterface.php
new file mode 100644
index 0000000..22eda08
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/Metadata/ElementInterface.php
@@ -0,0 +1,94 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\Core\Config\Metadata\ElementInterface.
+ */
+
+namespace Drupal\Core\Config\Metadata;
+
+use Drupal\Core\TypedData\ContextAwareInterface;
+use Drupal\Core\TypedData\TypedDataInterface;
+use ArrayAccess;
+use Countable;
+use Traversable;
+
+/**
+ * Interface for data structures that contain configuration data and metadata.
+ */
+interface ElementInterface extends Traversable, ArrayAccess, Countable, TypedDataInterface, ContextAwareInterface {
+
+  /**
+   * Gets configuration key for this object.
+   *
+   * @return string
+   *   Configuration key for this structure.
+   */
+  public function getKey();
+
+  /**
+   * Gets human readable label for this structure or children of it.
+   *
+   * @return string
+   *   The object label.
+   */
+  public function getLabel();
+
+  /**
+   * Gets raw metadata array for this element.
+   *
+   * The element's metadata is an array that may contain the following
+   * elements:
+   * - Any of the keys used for typed data definition prefixed by a dot.
+   * - Any nested array that will keyed by configuration key and will be mapped
+   *  to a nested ElementInterface or TypedDataInterface element.
+   *
+   * Example metadata from module/system/meta/system.site.yml
+   *
+   *   name:
+   *     .label: 'Site name'
+   *     .type: 'label'
+   *   mail:
+   *     .label: 'Site mail'
+   *   slogan:
+   *     .label: 'Site slogan'
+   *     .type: 'text'
+   *   page:
+   *     .list: '1'
+   *     403:
+   *       .label: 'Default 403 (access denied) page'
+   *       .type: 'string'
+   *     404:
+   *       .label: 'Default 404 (not found) page'
+   *       .type: 'string'
+   *     front:
+   *       .label: 'Default front page'
+   *       .type: 'string'
+   *
+   * @see Drupal\Core\TypedData\TypedDataManager::create().
+   *
+   * @return array
+   *   The full metadata array for this element.
+   */
+  public function getMetadata();
+
+  /**
+   * Sets the metadata array for the element.
+   *
+   * @param array $metadata
+   *   Array configuration metadata.
+   *
+   * @see getMetadata().
+   */
+  public function setMetadata($metadata);
+
+  /**
+   * Gets all contained typed data properties as plain array.
+   *
+   * @return array
+   *   List of TypedDataInterface objects indexed by full name (keys with dot
+   *   notation).
+   */
+  public function toList();
+
+}
diff --git a/core/lib/Drupal/Core/Config/Metadata/ListElement.php b/core/lib/Drupal/Core/Config/Metadata/ListElement.php
index 595ad07..9339568 100644
--- a/core/lib/Drupal/Core/Config/Metadata/ListElement.php
+++ b/core/lib/Drupal/Core/Config/Metadata/ListElement.php
@@ -8,54 +8,58 @@
 namespace Drupal\Core\Config\Metadata;
 
 use Drupal\Core\TypedData\ListInterface;
-use ArrayAccess;
-use Countable;
 
 /**
- * Defines configuration element wrapper that is a list of properties.
+ * Defines a 'configuration wrapper' that contains a list of elements.
  *
- * This is a nested element that wraps a generic array or list in the
+ * This is a configuration element that wraps a list of nested elements in the
  * configuration data.
+ *
+ * Supported list settings (below the definition's 'list settings' key) are:
+ * - 'elements_name', Configuration name for each of the nested elements, may
+ *   contain the placeholder '%' to replace by the element's key.
+ * - 'elements_key', Name of the configuration data property to be used as the
+ *   key for name replacement.
+ * - 'elements_label', Name of the configuration data property to be used as
+ *   the label for the element definition.
  */
-class ListElement extends NestedElement implements ListInterface {
-
-  /**
-   * Implements ArrayAccess::offsetExists().
-   */
-  public function offsetExists($offset) {
-    $data = $this->getElementData($offset);
-    return isset($data);
-  }
-
-  /**
-   * Implements ArrayAccess::offsetGet().
-   */
-  public function offsetGet($offset) {
-    return $this->buildElement($offset);
-  }
+class ListElement extends ElementBase implements ListInterface {
 
   /**
-   * Implements ArrayAccess::offsetSet().
+   * Overrides Drupal\Core\Config\Metadata\ElementBase::buildElementMetadata().
    */
-  public function offsetSet($offset, $value) {
-    if ($value instanceof TypedDataInterface) {
-      $value = $value->getValue();
+  protected function buildElementMetadata($key, $data) {
+    $meta = parent::buildElementMetadata($key, $data);
+    // When the parent element is a list, elements may have special settings.
+    if (isset($this->definition['list settings'])) {
+      $settings = $this->definition['list settings'];
+      if (isset($settings['elements_base']) && $base = config_metadata($settings['elements_base'])) {
+        // Load common base metadata for all elements.
+        $meta = Metadata::mergeDeep($base, $meta);
+      }
+      if (isset($settings['elements_name'])) {
+        // Load specific metadata for each element.
+        $name = $settings['elements_name'];
+        $element_key = $key;
+        if (isset($settings['elements_key'])) {
+          // The search key for this one is in the data itself.
+          $element_key = isset($data[$settings['elements_key']]) ? $data[$settings['elements_key']] : NULL;
+        }
+        if ($element_key) {
+          $name = str_replace('%', $element_key, $name);
+        }
+        if ($merge = config_metadata($name)) {
+          $meta = Metadata::mergeDeep($meta, $merge);
+        }
+      }
+      if (isset($settings['elements_label']) && !isset($meta['.label'])) {
+        // Extract element's label from configuration data.
+        if (!empty($data[$settings['elements_label']])) {
+          $meta['.label'] = $data[$settings['elements_label']];
+        }
+      }
     }
-    $this->setElementData($offset, $value);
-  }
-
-  /**
-   * Implements ArrayAccess::offsetUnset().
-   */
-  public function offsetUnset($offset) {
-    $this->clearElementData($offset);
-  }
-
-  /**
-   * Implements Countable::count().
-   */
-  public function count() {
-    return count($this->getData());
+    return $meta;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Config/Metadata/Metadata.php b/core/lib/Drupal/Core/Config/Metadata/Metadata.php
new file mode 100644
index 0000000..ce773a4
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/Metadata/Metadata.php
@@ -0,0 +1,85 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\Core\Config\Metadata\Metadata.
+ */
+
+namespace Drupal\Core\Config\Metadata;
+
+use Drupal\Component\Utility\NestedArray;
+
+/**
+ * Provides helpers to perform operations on arrays of configuration metadata.
+ */
+class Metadata extends NestedArray {
+
+  /**
+   * Builds a typed data element configuration data and metadata.
+   *
+   * @param mixed $value
+   *   Configuration data to be used as value.
+   * @param array $metadata
+   *   Metadata for the element.
+   * @param string $key
+   *   Nested configuration key to be used as element's name.
+   * @param Drupal\Core\Config\Metadata\ElementInterface $parent
+   *   (optional) Element to be used as parent of this one. Defaults to NULL.
+   *
+   * @return Drupal\Core\TypedData\TypedDataInterface
+   *   A TypedDataInterface object containing the configuration value.
+   */
+  public static function buildElement($value, $metadata, $key, $parent = NULL) {
+    $definition = self::buildDefinition($value, $metadata);
+    $context = array('name' => $key, 'parent' => $parent);
+    $element = typed_data()->create($definition, $value, $context);
+    if ($element instanceof ElementInterface) {
+      // If this is a nested ConfigElement we need to set the metadata for it.
+      $element->setMetadata($metadata);
+    }
+    return $element;
+  }
+
+  /**
+   * Builds element definition from metadata.
+   *
+   * @param mixed $data
+   *   The configuration data for the element.
+   *
+   * @param array $metadata
+   *   The raw metadata array for the element.
+   *
+   * @return array
+   *   The elemement's data definition.
+   */
+  public static function buildDefinition($data, $metadata) {
+    $element = $children = array();
+    foreach ($metadata as $name => $value) {
+      if (strpos($name, '.') === 0) {
+        // Metadata properties will be prefixed by a dot.
+        $element[substr($name, 1)] = $value;
+      }
+      else {
+        // Children elements will be arrays of metadata themselves.
+        $children[$name] = $value;
+      }
+    }
+    // The default type will depend on whether we've got children or not.
+    if (!isset($element['type'])) {
+      if (!empty($children) || is_array($data) || !empty($element['list']) || !empty($element['list settings'])) {
+        $element['type'] = 'config_element';
+      }
+      else {
+        $element['type'] = 'string';
+      }
+    }
+    if (isset($element['settings'])) {
+      // The element label may be contained in the data.
+      if (isset($element['settings']['label']) && isset($data[$element['settings']['label']])) {
+        $element['label'] = $data[$element['settings']['label']];
+      }
+    }
+    return $element;
+  }
+
+}
\ No newline at end of file
diff --git a/core/lib/Drupal/Core/Config/Metadata/NestedElement.php b/core/lib/Drupal/Core/Config/Metadata/NestedElement.php
deleted file mode 100644
index f800536..0000000
--- a/core/lib/Drupal/Core/Config/Metadata/NestedElement.php
+++ /dev/null
@@ -1,174 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\Config\Metadata\NestedElement.
- */
-
-namespace Drupal\Core\Config\Metadata;
-
-use Drupal\Core\Language\Language;
-use Drupal\Core\TypedData\TypedDataInterface;
-use Drupal\Core\TypedData\ContextAwareInterface;
-use Drupal\Component\Utility\NestedArray;
-
-/**
- * Defines a generic nested configuration wrapper element.
- *
- * Wraps configuration data belonging to an intermediate level of the array.
- * This object is contained in another NestedElement or the a ConfigWrapper.
- */
-class NestedElement extends WrapperBase implements TypedDataInterface, ContextAwareInterface {
-
-  /**
-   * The configuration key relative to the parent's.
-   *
-   * @var string
-   */
-  protected $key;
-
-  /**
-   * The definition for this typed data.
-   *
-   * @var array
-   */
-  protected $definition;
-
-  /**
-   * Parent configuration wrapper.
-   *
-   * @var Drupal\Core\Config\WrapperInterface
-   */
-  protected $parent;
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::__construct().
-   */
-  public function __construct(array $definition) {
-    $this->definition = $definition;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::setData().
-   */
-  public function setData($value) {
-    $this->data = $value;
-    $this->getParent()->setElementData($this->key, $this->data);
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::setElementData()
-   */
-  public function setElementData($key, $value) {
-    parent::setElementData($key, $value);
-    $this->getParent()->setElementData($this->key, $this->data);
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getKey().
-   */
-  public function getKey() {
-    $parent = $this->getParent()->getKey();
-    return ($parent || is_numeric($parent) ? $parent . '.' : '') . $this->key;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getMetadata().
-   */
-  public function getMetadata() {
-    return $this->getParent()->getElementMetadata($this->key);
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getBase().
-   */
-  public function getBase() {
-    return $this->getDefinition();
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::clearElementData()
-  */
-  public function clearElementData($key) {
-    parent::clearElementData($key);
-    $this->getParent()->setElementData($this->key, $data);
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::getType().
-   */
-  public function getType() {
-    return $this->definition['type'];
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::getDefinition().
-   */
-  public function getDefinition() {
-    return $this->definition;
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::getValue().
-   */
-  public function getValue() {
-    return $this->getData();
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::setValue().
-   */
-  public function setValue($value) {
-    $this->data = $value;
-    // Due to how the constructor works, this function may get called before
-    // the parent is set.
-    // @see Drupal\Core\TypedData\TypedDataManager::createInstance()
-    if ($this->getParent()) {
-      $this->getParent()->set($this->key, $value);
-    }
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::getString().
-   */
-  public function getString() {
-    return (string) $this->getValue();
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\TypedDataInterface::validate().
-   */
-  public function validate() {
-    // This will be ok if we have any config data at all.
-    return isset($this->data);
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ContextAwareInterface::getName().
-   */
-  public function getName() {
-    return $this->key;
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ContextAwareInterface::setName().
-   */
-  public function setName($name) {
-    $this->key = $name;
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ContextAwareInterface::getParent().
-  */
-  public function getParent() {
-    return $this->parent;
-  }
-
-  /**
-   * Implements Drupal\Core\TypedData\ContextAwareInterface::setParent().
-  */
-  public function setParent($parent) {
-    $this->parent = $parent;
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Config/Metadata/WrapperBase.php b/core/lib/Drupal/Core/Config/Metadata/WrapperBase.php
deleted file mode 100644
index 737a620..0000000
--- a/core/lib/Drupal/Core/Config/Metadata/WrapperBase.php
+++ /dev/null
@@ -1,299 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\Config\Metadata\WrapperBase.
- */
-
-namespace Drupal\Core\Config\Metadata;
-
-use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\TypedData\ListInterface;
-use ArrayIterator;
-use IteratorAggregate;
-
-/**
- * Base class for all configuration data wrappers.
- */
-abstract class WrapperBase implements IteratorAggregate, WrapperInterface {
-
-  /**
-   * The configuration data.
-   *
-   * @var array
-   */
-  protected $data;
-
-  /**
-   * Cached metadata for elements.
-   *
-   * @var array
-   */
-  protected $metadata;
-
-  /**
-   * Builds properties using configuration data and metadata.
-   *
-   * @param string $key
-   *   Configuration key.
-   *
-   * @return Drupal\Core\TypedData\TypedDataInterface
-   *   A TypedDataInterface object containing the configuration value.
-   */
-  protected function buildElement($key) {
-    // Build element array to start with.
-    $definition = $this->getElementDefinition($key);
-    $value = $this->getElementData($key);
-    // If this is an end property, the value will be the configuration data.
-    // If it is a NestedElement, it won't be set, but retrieved from the parent
-    // element. See NestedElement::setValue()
-    $context = array('name' => $key, 'parent' => $this);
-    return typed_data()->create($definition, $value, $context);
-  }
-
-  /**
-   * Builds metadata for a child element.
-   *
-   * @param $key
-   *   Element's key.
-   *
-   * @return array
-   *   Configuration metadata for the element.
-   */
-  protected function buildElementMetadata($key) {
-    $metadata = $this->getMetadata();
-    $meta = isset($metadata[$key]) ? $metadata[$key] : array();
-    $definition = $this->getBase();
-    $constraints = isset($definition['constraints']) ? $definition['constraints'] : array();
-    if (isset($constraints['elements_base']) && $base = config_metadata($constraints['elements_base'])) {
-      // Load common base metadata for all elements.
-      $meta = NestedArray::mergeDeep($base, $meta);
-    }
-    if (isset($constraints['elements_name'])) {
-      // Load specific metadata for each element.
-      $name = $constraints['elements_name'];
-      $element_key = $key;
-      if (isset($constraints['elements_key'])) {
-        // The search key for this one is in the data itself.
-        $key_name = str_replace('%', $key, $constraints['elements_key']);
-
-        $element_key = $this->getElementData($key_name);
-      }
-      if ($element_key) {
-        $name = str_replace('%', $element_key, $name);
-      }
-      if ($merge = config_metadata($name)) {
-        $meta = NestedArray::mergeDeep($meta, $merge);
-      }
-    }
-    if (isset($constraints['elements_label']) && !isset($meta['.label'])) {
-      // Extract element's label from configuration data.
-      $key_name = str_replace('%', $key, $constraints['elements_label']);
-      if ($label = $this->getElementData($key_name)) {
-        $meta['.label'] = $label;
-      }
-    }
-    return $meta;
-  }
-
-  /**
-   * Builds element definition from metadata.
-   *
-   * @param mixed $data
-   *   The configuration data for the element.
-   *
-   * @param array $metadata
-   *   The raw metadata array for the element.
-   *
-   * @return array
-   *   The elemement's data definition.
-   */
-  protected function buildDefinition($data, $metadata) {
-    $element = $children = array();
-    foreach ($metadata as $name => $value) {
-      if (strpos($name, '.') === 0) {
-        // Metadata properties will be prefixed by a dot.
-        $element[substr($name, 1)] = $value;
-      }
-      else {
-        // Children elements will be arrays of metadata themselves.
-        $children[$name] = $value;
-      }
-    }
-    // The default type will depend on whether we've got children or not.
-    if (!isset($element['type'])) {
-      if (!empty($children) || is_array($data) || !empty($element['list'])) {
-        $element['type'] = 'config_element';
-        $element['list'] = TRUE;
-      }
-      else {
-        $element['type'] = 'string';
-      }
-    }
-    return $element;
-  }
-
-  /**
-   * Gets valid configuration data keys.
-   *
-   * @return array
-   *   Array of valid configuration data keys.
-   */
-  protected function getAllKeys() {
-    return is_array($this->data) ? array_keys($this->data) : array();
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getData().
-   */
-  public function getData() {
-    return $this->data;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::setData().
-   */
-  public function setData($value) {
-    $this->data = $value;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getLabel().
-   */
-  public function getLabel() {
-    $definition = $this->getBase();
-    return isset($definition['label']) ? $definition['label'] : $this->getKey();
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElement().
-   */
-  public function getElement($key) {
-    $parts = explode('.', $key);
-    $first = array_shift($parts);
-    $data = $this->getElementData($first);
-    // Only attempt to build the element if it actually has configuration data.
-    if (isset($data) && $element = $this->buildElement($first)) {
-      $subkey = implode('.', $parts);
-      // If not a nested key, return the element whatever it is. But if we need
-      // to find a nested key, this is only possible if it's a WrapperInterface.
-      if (!$subkey) {
-        return $element;
-      }
-      elseif ($element instanceof WrapperInterface) {
-        return $element->getElement($subkey);
-      }
-    }
-    return NULL;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::setElementData().
-   */
-  public function setElementData($key, $value) {
-    $parts = explode('.', $key);
-    if (count($parts) == 1) {
-      $this->data[$key] = $value;
-    }
-    else {
-      NestedArray::setValue($this->data, $parts, $value);
-    }
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElementData().
-   */
-  public function getElementData($key) {
-    $parts = explode('.', $key);
-    if (count($parts) == 1) {
-      return isset($this->data[$key]) ? $this->data[$key] : NULL;
-    }
-    else {
-      $value = NestedArray::getValue($this->data, $parts, $key_exists);
-      return $key_exists ? $value : NULL;
-    }
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElementDefinition().
-   */
-  public function getElementDefinition($key) {
-    return $this->buildDefinition($this->getElementData($key), $this->getElementMetadata($key));
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElementMetadata().
-   */
-  public function getElementMetadata($key) {
-    // Metadata for nested elements must be built before.
-    if (!isset($this->metadata[$key])) {
-      $this->metadata[$key] = $this->buildElementMetadata($key);
-    }
-    return $this->metadata[$key];
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElementLabel().
-   */
-  public function getElementLabel($key) {
-    $definition = $this->getElementDefinition($key);
-    return isset($definition['label']) ? $definition['label'] : $this->getElementKey($key);
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::getElementKey().
-   */
-  public function getElementKey($key) {
-    $parent = $this->getKey();
-    return $parent ? $parent . '.' . $key : $key;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::clearElementData().
-   */
-  public function clearElementData($key) {
-    $parts = explode('.', $key);
-    if (count($parts) == 1) {
-      unset($this->data[$key]);
-    }
-    else {
-      NestedArray::unsetValue($this->data, $parts);
-    }
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::toArray().
-   */
-  public function toArray() {
-    $array = array();
-    foreach ($this->getAllKeys() as $key) {
-      $array[$key] = $this->buildElement($key);
-    }
-    return $array;
-  }
-
-  /**
-   * Implements Drupal\Core\Config\Metadata\WrapperInterface::toList().
-   */
-  public function toList($base_name = '') {
-    $list = array();
-    foreach ($this->toArray() as $key => $element) {
-      $name = $base_name ? $base_name . '.' . $key : $key;
-      if ($element instanceof WrapperInterface) {
-        $list += $element->toList($name);
-      }
-      else {
-        $list[$name] = $element;
-      }
-    }
-    return $list;
-  }
-
-  /**
-   * Implements IteratorAggregate::getIterator().
-   */
-  public function getIterator() {
-    return new ArrayIterator($this->toArray());
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Config/Metadata/WrapperInterface.php b/core/lib/Drupal/Core/Config/Metadata/WrapperInterface.php
deleted file mode 100644
index fd4bf6f..0000000
--- a/core/lib/Drupal/Core/Config/Metadata/WrapperInterface.php
+++ /dev/null
@@ -1,212 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\Config\Metadata\WrapperInterface.
- */
-
-namespace Drupal\Core\Config\Metadata;
-
-use Drupal\Core\TypedData\ComplexDataInterface;
-
-/**
- * Interface for data structures that contain configuration data and metadata.
- */
-interface WrapperInterface {
-
-  /**
-   * Gets configuration key for this object.
-   *
-   * @return string
-   *   Configuration key for this structure.
-   */
-  public function getKey();
-
-  /**
-   * Gets human readable label for this structure or children of it.
-   *
-   * @return string
-   *   The object label.
-   */
-  public function getLabel();
-
-  /**
-   * Gets raw configuration data for this element.
-   *
-   * @return mixed
-   *   The configuration data for this element.
-   */
-  public function getData();
-
-  /**
-   * Gets typed data definition for the object.
-   *
-   * @return array
-   *   The configuration data for this element.
-   */
-  public function getBase();
-
-  /**
-   * Sets raw configuration data.
-   *
-   * @param $value
-   *   Value to set in the configuration data.
-   */
-  public function setData($value);
-
-  /**
-   * Gets raw metadata array for this element.
-   *
-   * @return array
-   *   The full metadata array for this element.
-   */
-  public function getMetadata();
-
-  /**
-   * Gets configuration key for element.
-   *
-   * @param $key
-   *   The element's key.
-   *
-   * @return string
-   *   Configuration key for this structure.
-   */
-  public function getElementKey($key);
-
-  /**
-   * Gets human readable label for element.
-   *
-   * @param $key
-   *   The element's key.
-   *
-   * @return string
-   *   The element's label.
-  */
-  public function getElementLabel($key);
-
-  /**
-   * Gets the built metadata array for a child element.
-   *
-   * The element's metadata is an array that may contain the following
-   * elements:
-   * - Any of the keys used by getElementDefinition() prefixed by a dot.
-   * - Any nested array that will keyed by configuration key and will be mapped
-   *  to a nested WrapperInterface or TypedDataInterface element.
-   *
-   * Example metadata from module/system/meta/system.site.yml
-   *
-   *   name:
-   *     .label: 'Site name'
-   *     .type: 'label'
-   *   mail:
-   *     .label: 'Site mail'
-   *   slogan:
-   *     .label: 'Site slogan'
-   *     .type: 'text'
-   *   page:
-   *     .list: '1'
-   *     403:
-   *       .label: 'Default 403 (access denied) page'
-   *       .type: 'string'
-   *     404:
-   *       .label: 'Default 404 (not found) page'
-   *       .type: 'string'
-   *     front:
-   *       .label: 'Default front page'
-   *       .type: 'string'
-   *
-   * @param $key
-   *   Key from the configuration data array.
-   *
-   * @return array
-   *   The metadata for the element, defaults to an empty array.
-   */
-  public function getElementMetadata($key);
-
-  /**
-   * Gets the definition array for a child element.
-   *
-   * The element definition is an array that may contain any of the following
-   * optional elements:
-   * - 'label', Human readable name for the element.
-   * - 'elements.name', Configuration name for each of the nested elements, may
-   *   contain the placeholder '%' to replace by the element's key.
-   * - 'elements.key', Name of the configuration data property to be used as the
-   *   key for name replacement. It may contain the placeholder '%' to be
-   *   replaced by the element's key.
-   * - 'elements.label', Name of the configuration data property to be used as
-   *   the label for the element definition. It may contain the placeholder '%'
-   *   to be replaced by the element's key.
-   * - Any of the keys used for the $definition parameter of
-   *   Drupal\Core\TypedData\TypedDataManager::create().
-   *
-   * @param $key
-   *   Key from the configuration data array.
-   *
-   * @return array
-   *   The definition for the element, defaults to an empty array.
-   */
-  public function getElementDefinition($key);
-
-  /**
-   * Gets a nested property object using a key with dot notation.
-   *
-   * @param string $key
-   *   Configuration key.
-   *
-   * @return \Drupal\Core\TypedData\TypedDataInterface|\Drupal\Core\TypedData\ListInterface|null
-   *   The property object or a list of property objects or null if the
-   *   property doesn't exist.
-   */
-  public function getElement($key);
-
-  /**
-   * Gets raw configuration for a child element.
-   *
-   * @param $key
-   *   (optional) Relative key within the configuration data.
-   *
-   * @return array|string|null
-   *   Array or item of configuration data.
-   */
-  public function getElementData($key);
-
-  /**
-   * Sets raw configuration data.
-   *
-   * @param $key
-   *   Relative key within the configuration data.
-   * @param $value
-   *   Value to set in the configuration data.
-   */
-  public function setElementData($key, $value);
-
-  /**
-   * Delete configuration data.
-   *
-   * @param $key
-   *   Relative key within the configuration data.
-   */
-  public function clearElementData($key);
-
-  /**
-   * Gets typed data properties as array.
-   *
-   * @return array
-   *   List of TypedDataInterface objects indexed by key.
-   */
-  public function toArray();
-
-  /**
-   * Gets all contained typed data properties as plain array.
-   *
-   * @param string $base_name
-   *   Base name to prepend to all of the element's names.
-   *
-   * @return array
-   *   List of TypedDataInterface objects indexed by full name (keys with dot
-   *   notation).
-   */
-  public function toList($base_name = '');
-
-}
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigMetadataTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigMetadataTest.php
index 831e7f4..30177b3 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigMetadataTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigMetadataTest.php
@@ -59,10 +59,10 @@ function testBasicMetadata() {
       ),
       'effects' => array(
         '.label' =>  'Style effects',
-        '.list' => 'true',
-        '.constraints' => array(
+        '.list' => '1',
+        '.list settings' => array(
           'elements_name' => 'image.style.effects.%',
-          'elements_key' => '%.name'
+          'elements_key' => 'name'
         ),
       )
     );
@@ -78,7 +78,6 @@ function testBasicMetadata() {
       ),
       'data' => array(
         '.label' => 'Data',
-        '.list' => 'true',
         'width' => array(
           '.label' => 'Width',
           '.type' => 'integer'
@@ -126,13 +125,18 @@ function testConfigMetadata() {
     $this->assertEqual(count($list), 3, 'Got a list with the right number of properties for site page data');
     $this->assertTrue(isset($list['front']) && isset($list['403']) && isset($list['404']), 'Got a list with the right properties for site page data.');
     $this->assertEqual($list['front']->getValue(), 'user', 'Got the right value for page.front data from the list.');
+    // And test some ComplexDataInterface methods.
+    $properties = $list->getProperties();
+    $this->assertTrue(count($properties) == 3 && $properties['front'] == $list['front'], 'Got the right properties for site page.');
+    $values = $list->getPropertyValues();
+    $this->assertTrue(count($values) == 3 && $values['front'] == 'user', 'Got the right property values for site page.');
 
     // Now let's try something more complex, with nested objects.
     $wrapper = config_wrapper('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');
-    $ieid = key($effects->toArray());
+    $ieid = key($effects->getValue());
     $effect = $wrapper->get('effects.' . $ieid);
     $this->assertTrue(count($effect['data']) && $effect['name']->getValue() == 'image_scale', 'Got data for the image scale effect from metadata.');
     $this->assertEqual($effect['data']['width']->getType(), 'integer', 'Got the right type for the scale effect width.');
@@ -142,7 +146,7 @@ function testConfigMetadata() {
     $this->assertEqual($effect['data']->getKey(), $key, 'Got the right configuration key for a nested image styple effect');
     $object = $wrapper->get($key);
     $this->assertEqual(get_class($effect['data']), get_class($object), 'Got the same object class using different keys with dot notation.');
-    $this->assertEqual($effect['data']->getData(), $object->getData(), 'Got the same object values using different keys with dot notation.');
+    $this->assertEqual($effect['data']->getValue(), $object->getValue(), 'Got the same object values using different keys with dot notation.');
 
     // Finally update some object using a configuration wrapper.
     $new_slogan = 'Site slogan for testing configuration metadata';
diff --git a/core/modules/contact/meta/contact.category.%.yml b/core/modules/contact/meta/contact.category.%.yml
index eb6226a..a0095d0 100644
--- a/core/modules/contact/meta/contact.category.%.yml
+++ b/core/modules/contact/meta/contact.category.%.yml
@@ -1,3 +1,5 @@
+.settings:
+  label: label
 id:
   .type: string
   .label: 'Id'
diff --git a/core/modules/image/meta/image.style.%.yml b/core/modules/image/meta/image.style.%.yml
index b5fcab1..5399fa4 100644
--- a/core/modules/image/meta/image.style.%.yml
+++ b/core/modules/image/meta/image.style.%.yml
@@ -7,6 +7,6 @@ label:
 effects:
   .label: 'Style effects'
   .list: '1'
-  .constraints:
+  .list settings:
     elements_name: 'image.style.effects.%'
-    elements_key: '%.name'
+    elements_key: 'name'
diff --git a/core/modules/image/meta/image.style.effects.%.yml b/core/modules/image/meta/image.style.effects.%.yml
index 42ef18b..2f73d81 100644
--- a/core/modules/image/meta/image.style.effects.%.yml
+++ b/core/modules/image/meta/image.style.effects.%.yml
@@ -3,7 +3,6 @@ name:
   .type: string
 data:
   .label: 'Data'
-  .list: '1'
 weight:
   .label: 'Weight'
   .type: integer
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleConfigWrapper.php b/core/modules/locale/lib/Drupal/locale/LocaleConfigWrapper.php
index 5a90d57..f16d913 100644
--- a/core/modules/locale/lib/Drupal/locale/LocaleConfigWrapper.php
+++ b/core/modules/locale/lib/Drupal/locale/LocaleConfigWrapper.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Language\Language;
 use Drupal\Core\Config\Metadata\ConfigWrapper;
-use Drupal\Core\Config\Metadata\WrapperInterface;
+use Drupal\Core\Config\Metadata\ElementInterface;
 use Drupal\Core\TypedData\TranslatableInterface;
 use InvalidArgumentException;
 
@@ -125,7 +125,7 @@ public function getTranslation($langcode, $strict = TRUE) {
         'strict' => $strict,
       );
       //$data = $source->getTranslatedData($this, $options);
-      $data = $this->getTranslatedData($this->toArray(), $options);
+      $data = $this->getTranslatedData($this->get(), $options);
       $translation = new LocaleConfigWrapper($this->name, $data);
       $translation->setTranslation($langcode, $strict, $this);
       return $translation;
@@ -147,8 +147,8 @@ public function language() {
   /**
    * Get translated configuration data.
    *
-   * @param array $elements
-   *   Array of configuration elements.
+   * @param Traversable $elements
+   *   Configuration elements.
    * @param array $options
    *   Array with options that will depend on the translator used.
    *
@@ -160,8 +160,8 @@ protected function getTranslatedData($elements, $options) {
     $translation = array();
     foreach ($elements as $key => $element) {
       $value = NULL;
-      if ($element instanceof WrapperInterface) {
-        $value = $this->getTranslatedData($element->toArray(), $options);
+      if ($element instanceof ElementInterface) {
+        $value = $this->getTranslatedData($element, $options);
       }
       elseif ($this->translateElement($element, $options)) {
         $value = $element->getValue();
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
index 40c27fc..765c314 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\locale\Tests;
 
+use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 use Drupal\locale\LocaleConfigWrapper;
 
@@ -41,7 +42,7 @@ function setUp() {
   function testConfigTranslation() {
     // Add custom language
     $langcode = 'xx';
-    $admin_user = $this->drupalCreateUser(array('administer languages', 'access administration pages'));
+    $admin_user = $this->drupalCreateUser(array('administer languages', 'access administration pages', 'translate interface'));
     $this->drupalLogin($admin_user);
     $name = $this->randomName(16);
     $edit = array(
@@ -51,28 +52,47 @@ function testConfigTranslation() {
       'direction' => '0',
     );
     $this->drupalPost('admin/config/regional/language/add', $edit, t('Add custom language'));
+    $language = new Language(array('langcode' => $langcode));
+    // Set path prefix.
+    $edit = array( "prefix[$langcode]" => $langcode );
+    $this->drupalPost('admin/config/regional/language/detection/url', $edit, t('Save configuration'));
 
     // Check site name string exists and create translation for it.
-    $site_name = $this->randomName(20);
     $string = $this->storage->findString(array('source' => 'Drupal', 'context' => '', 'type' => 'configuration'));
     $this->assertTrue($string, 'Configuration strings have been created upon installation.');
-    $this->storage
-      ->createTranslation(array('lid' => $string->lid, 'language' => $langcode, 'translation' => $site_name))
-      ->save();
+
+    // Translate using the UI so configuration is refreshed.
+    $site_name = $this->randomName(20);
+    $search = array(
+      'string' => $string->source,
+      'langcode' => $langcode,
+      'translation' => 'all',
+    );
+    $this->drupalPost('admin/config/regional/translate/translate', $search, t('Filter'));
+    $textarea = current($this->xpath('//textarea'));
+    $lid = (string) $textarea[0]['name'];
+    $edit = array(
+      $lid => $site_name,
+    );
+    $this->drupalPost('admin/config/regional/translate/translate', $edit, t('Save translations'));
 
     $data = config('system.site')->get();
     $wrapper = new LocaleConfigWrapper('system.site', $data, $this->storage);
 
     // Get strict translation and check we've got only the site name.
     $translation = $wrapper->getTranslation($langcode, TRUE);
-    $properties = $translation->toList();
+    $properties = $translation->get()->toList();
     $this->assertEqual(count($properties), 1, 'Got the right number of properties with strict translation');
     $this->assertEqual($properties['name']->getValue(), $site_name, 'Got the right translation for site name with strict translation');
     // Get non strict translation and check we've got all properties.
     $translation = $wrapper->getTranslation($langcode, FALSE);
-    $properties = $translation->toList();
+    $properties = $translation->get()->toList();
     $this->assertEqual(count($properties), 6, 'Got the right number of properties with non strict translation');
     $this->assertEqual($properties['name']->getValue(), $site_name, 'Got the right translation for site name with non strict translation');
+
+    // Check the translated site name is displayed.
+    $this->drupalGet($langcode);
+    $this->assertText($site_name, 'The translated site name is displayed after translations refreshed.');
   }
 
 }
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 8e01943..e69e138 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -14,7 +14,6 @@
 use Drupal\Core\Config\InstallStorage;
 use Drupal\Core\Config\StorageException;
 
-
 /**
  * Form constructor for the translation import screen.
  *
diff --git a/core/modules/system/meta/system.site.yml b/core/modules/system/meta/system.site.yml
index f95f546..8476bdf 100644
--- a/core/modules/system/meta/system.site.yml
+++ b/core/modules/system/meta/system.site.yml
@@ -7,7 +7,6 @@ slogan:
   .label: 'Site slogan'
   .type: text
 page:
-  .list: '1'
   .label: 'Default pages'
   403:
     .label: 'Default 403 (access denied) page'
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 72894c8..ac458d5 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2113,9 +2113,9 @@ function system_data_type_info() {
       'list class' => '\Drupal\Core\Entity\Field\Type\Field',
     ),
     'config_element' => array(
-      'label' => t('Nested configuration'),
-      'description' => t('Nested configuration data'),
-      'class' => 'Drupal\Core\Config\Metadata\NestedElement',
+      'label' => t('Configuration element'),
+      'description' => t('Configuration data'),
+      'class' => 'Drupal\Core\Config\Metadata\ConfigElement',
       'list class' => 'Drupal\Core\Config\Metadata\ListElement',
     ),
     // These are UI string types.
diff --git a/core/modules/user/meta/user.mail.yml b/core/modules/user/meta/user.mail.yml
index d25633c..5a3e9bb 100644
--- a/core/modules/user/meta/user.mail.yml
+++ b/core/modules/user/meta/user.mail.yml
@@ -1,4 +1,4 @@
 .label: 'User mails'
 .list: '1'
-.constraints:
+.list settings:
   elements_name: 'user.mail.%'