diff --git a/src/Form/IndexForm.php b/src/Form/IndexForm.php
index 3bf8bb6..38b3266 100644
--- a/src/Form/IndexForm.php
+++ b/src/Form/IndexForm.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
 use Drupal\search_api\Datasource\DatasourcePluginManager;
 use Drupal\search_api\IndexInterface;
 use Drupal\search_api\SearchApiException;
@@ -305,8 +306,8 @@ public function buildEntityForm(array &$form, FormStateInterface $form_state, In
       '#type' => 'radios',
       '#title' => $this->t('Server'),
       '#description' => $this->t('Select the server this index should use. Indexes cannot be enabled without a connection to a valid, enabled server.'),
-      '#options' => array(NULL => '<em>' . $this->t('- No server -') . '</em>') + $this->getServerOptions(),
-      '#default_value' => $index->hasValidServer() ? $index->getServerId() : NULL,
+      '#options' => array('' => '<em>' . $this->t('- No server -') . '</em>') + $this->getServerOptions(),
+      '#default_value' => $index->hasValidServer() ? $index->getServerId() : '',
     );
 
     $form['status'] = array(
@@ -374,15 +375,18 @@ public function buildEntityForm(array &$form, FormStateInterface $form_state, In
    */
   public function buildDatasourcesConfigForm(array &$form, FormStateInterface $form_state, IndexInterface $index) {
     foreach ($index->getDatasources() as $datasource_id => $datasource) {
-      // @todo Create, use and save SubFormState already here, not only in
-      //   validate(). Also, use proper subset of $form for first parameter?
-      if ($config_form = $datasource->buildConfigurationForm(array(), $form_state)) {
+      $form['datasource_configs'] += array($datasource_id => array());
+      $datasource_form_state = SubformState::createForSubform($form['datasource_configs'][$datasource_id], $form, $form_state);
+      if ($config_form = $datasource->buildConfigurationForm($form['datasource_configs'][$datasource_id], $datasource_form_state)) {
         $form['datasource_configs'][$datasource_id]['#type'] = 'details';
         $form['datasource_configs'][$datasource_id]['#title'] = $this->t('Configure the %datasource datasource', array('%datasource' => $datasource->getPluginDefinition()['label']));
         $form['datasource_configs'][$datasource_id]['#open'] = $index->isNew();
 
         $form['datasource_configs'][$datasource_id] += $config_form;
       }
+      else {
+        unset($form['datasource_configs'][$datasource_id]);
+      }
     }
   }
 
@@ -395,9 +399,9 @@ public function buildDatasourcesConfigForm(array &$form, FormStateInterface $for
   public function buildTrackerConfigForm(array &$form, FormStateInterface $form_state, IndexInterface $index) {
     if ($index->hasValidTracker()) {
       $tracker = $index->getTrackerInstance();
-      // @todo Create, use and save SubFormState already here, not only in
-      //   validate(). Also, use proper subset of $form for first parameter?
-      if ($config_form = $tracker->buildConfigurationForm(array(), $form_state)) {
+      $form += array('tracker_config' => array());
+      $tracker_form_state = SubformState::createForSubform($form['tracker_config'], $form, $form_state);
+      if ($config_form = $tracker->buildConfigurationForm(array(), $tracker_form_state)) {
         $form['tracker_config']['#type'] = 'details';
         $form['tracker_config']['#title'] = $this->t('Configure %plugin', array('%plugin' => $tracker->label()));
         $form['tracker_config']['#description'] = Html::escape($tracker->getDescription());
@@ -405,6 +409,9 @@ public function buildTrackerConfigForm(array &$form, FormStateInterface $form_st
 
         $form['tracker_config'] += $config_form;
       }
+      else {
+        unset($form['tracker_config']);
+      }
     }
     // Only notify the user of a missing tracker plugin if we're editing an
     // existing index.
@@ -435,7 +442,7 @@ public function buildAjaxDatasourceConfigForm(array $form, FormStateInterface $f
    *
    * Takes care of changes in the selected tracker plugin.
    */
-  public function submitAjaxTrackerConfigForm($form, FormStateInterface $form_state) {
+  public function submitAjaxTrackerConfigForm(array $form, FormStateInterface $form_state) {
     $form_state->setValue('id', NULL);
     $form_state->setRebuild();
   }
@@ -475,9 +482,10 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     /** @var \Drupal\search_api\Datasource\DatasourceInterface[] $datasource_plugins */
     $datasource_plugins = $this->originalEntity->getDatasources(FALSE);
     foreach ($datasource_ids as $datasource_id) {
-      $datasource_form = (!empty($form['datasource_configs'][$datasource_id])) ? $form['datasource_configs'][$datasource_id] : array();
-      $datasource_form_state = new SubFormState($form_state, array('datasource_configs', $datasource_id));
-      $datasource_plugins[$datasource_id]->validateConfigurationForm($datasource_form, $datasource_form_state);
+      if (!empty($form['datasource_configs'][$datasource_id])) {
+        $datasource_form_state = SubformState::createForSubform($form['datasource_configs'][$datasource_id], $form, $form_state);
+        $datasource_plugins[$datasource_id]->validateConfigurationForm($form['datasource_configs'][$datasource_id], $datasource_form_state);
+      }
     }
 
     // Call validateConfigurationForm() for the (possibly new) tracker.
@@ -493,8 +501,10 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     else {
       $tracker = $this->trackerPluginManager->createInstance($tracker_id, array('index' => $this->originalEntity));
     }
-    $tracker_form_state = new SubFormState($form_state, array('tracker_config'));
-    $tracker->validateConfigurationForm($form['tracker_config'], $tracker_form_state);
+    if (!empty($form['tracker_config'])) {
+      $tracker_form_state = SubformState::createForSubform($form['tracker_config'], $form, $form_state);
+      $tracker->validateConfigurationForm($form['tracker_config'], $tracker_form_state);
+    }
   }
 
   /**
@@ -533,9 +543,10 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     $datasource_settings = array();
     foreach ($datasources as $datasource_id) {
       $datasource = $datasource_plugins[$datasource_id];
-      $datasource_form = (!empty($form['datasource_configs'][$datasource_id])) ? $form['datasource_configs'][$datasource_id] : array();
-      $datasource_form_state = new SubFormState($form_state, array('datasource_configs', $datasource_id));
-      $datasource->submitConfigurationForm($datasource_form, $datasource_form_state);
+      if (!empty($form['datasource_configs'][$datasource_id])) {
+        $datasource_form_state = SubformState::createForSubform($form['datasource_configs'][$datasource_id], $form, $form_state);
+        $datasource->submitConfigurationForm($form['datasource_configs'][$datasource_id], $datasource_form_state);
+      }
 
       $datasource_settings[$datasource_id] = $datasource;
     }
@@ -555,8 +566,10 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       $tracker = $this->trackerPluginManager->createInstance($tracker_id, array('index' => $this->originalEntity));
     }
 
-    $tracker_form_state = new SubFormState($form_state, array('tracker_config'));
-    $tracker->submitConfigurationForm($form['tracker_config'], $tracker_form_state);
+    if (!empty($form['tracker_config'])) {
+      $tracker_form_state = SubformState::createForSubform($form['tracker_config'], $form, $form_state);
+      $tracker->submitConfigurationForm($form['tracker_config'], $tracker_form_state);
+    }
     $index->setTracker($tracker);
   }
 
diff --git a/src/Form/IndexProcessorsForm.php b/src/Form/IndexProcessorsForm.php
index 5ffffe8..fa2ffe1 100644
--- a/src/Form/IndexProcessorsForm.php
+++ b/src/Form/IndexProcessorsForm.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
 use Drupal\search_api\Processor\ProcessorInterface;
 use Drupal\search_api\Processor\ProcessorPluginManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -211,23 +212,25 @@ public function form(array $form, FormStateInterface $form_state) {
     );
 
     foreach ($all_processors as $processor_id => $processor) {
-      $sub_keys = array('processors', $processor_id, 'settings');
-      $processor_form_state = new SubFormState($form_state, $sub_keys);
-      $processor_form = $processor->buildConfigurationForm($form, $processor_form_state);
-      if ($processor_form) {
-        $form['settings'][$processor_id] = array(
-          '#type' => 'details',
-          '#title' => $processor->label(),
-          '#group' => 'processor_settings',
-          '#parents' => array('processors', $processor_id, 'settings'),
-          '#attributes' => array(
-            'class' => array(
-              'search-api-processor-settings-' . Html::cleanCssIdentifier($processor_id),
-            ),
+      $form['settings'][$processor_id] = array(
+        '#type' => 'details',
+        '#title' => $processor->label(),
+        '#group' => 'processor_settings',
+        '#parents' => array('processors', $processor_id, 'settings'),
+        '#attributes' => array(
+          'class' => array(
+            'search-api-processor-settings-' . Html::cleanCssIdentifier($processor_id),
           ),
-        );
+        ),
+      );
+      $processor_form_state = SubformState::createForSubform($form['settings'][$processor_id], $form, $form_state);
+      $processor_form = $processor->buildConfigurationForm($form['settings'][$processor_id], $processor_form_state);
+      if ($processor_form) {
         $form['settings'][$processor_id] += $processor_form;
       }
+      else {
+        unset($form['settings'][$processor_id]);
+      }
     }
 
     return $form;
@@ -246,8 +249,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     // Iterate over all processors that have a form and are enabled.
     foreach ($form['settings'] as $processor_id => $processor_form) {
       if (!empty($values['status'][$processor_id])) {
-        $sub_keys = array('processors', $processor_id, 'settings');
-        $processor_form_state = new SubFormState($form_state, $sub_keys);
+        $processor_form_state = SubformState::createForSubform($form['settings'][$processor_id], $form, $form_state);
         $processors[$processor_id]->validateConfigurationForm($form['settings'][$processor_id], $processor_form_state);
       }
     }
@@ -279,8 +281,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       );
       $processor_values = $values['processors'][$processor_id];
       if (isset($form['settings'][$processor_id])) {
-        $sub_keys = array('processors', $processor_id, 'settings');
-        $processor_form_state = new SubFormState($form_state, $sub_keys);
+        $processor_form_state = SubformState::createForSubform($form['settings'][$processor_id], $form, $form_state);
         $processor->submitConfigurationForm($form['settings'][$processor_id], $processor_form_state);
         $new_settings[$processor_id]['settings'] = $processor->getConfiguration();
         $new_settings[$processor_id]['settings'] += array('index' => $this->entity);
diff --git a/src/Form/ServerForm.php b/src/Form/ServerForm.php
index a515c64..3abb2a3 100644
--- a/src/Form/ServerForm.php
+++ b/src/Form/ServerForm.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
 use Drupal\Core\Url;
 use Drupal\search_api\Backend\BackendPluginManager;
 use Drupal\search_api\SearchApiException;
@@ -211,7 +212,8 @@ public function buildBackendConfigForm(array &$form, FormStateInterface $form_st
 
     if ($server->hasValidBackend()) {
       $backend = $server->getBackend();
-      if (($backend_form = $backend->buildConfigurationForm(array(), $form_state))) {
+      $backend_form_state = SubformState::createForSubform($form['backend_config'], $form, $form_state);
+      if (($backend_form = $backend->buildConfigurationForm($form['backend_config'], $backend_form_state))) {
         // If the backend plugin changed, notify the user.
         if (!empty($form_state->getValues()['backend'])) {
           drupal_set_message($this->t('Please configure the used backend.'), 'warning');
@@ -267,7 +269,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     }
     // Check before loading the backend plugin so we don't throw an exception.
     elseif ($form['backend_config']['#type'] == 'details' && $server->hasValidBackend()) {
-      $backend_form_state = new SubFormState($form_state, array('backend_config'));
+      $backend_form_state = SubformState::createForSubform($form['backend_config'], $form, $form_state);
       $server->getBackend()->validateConfigurationForm($form['backend_config'], $backend_form_state);
     }
   }
@@ -282,7 +284,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     $server = $this->getEntity();
     // Check before loading the backend plugin so we don't throw an exception.
     if ($form['backend_config']['#type'] == 'details' && $server->hasValidBackend()) {
-      $backend_form_state = new SubFormState($form_state, array('backend_config'));
+      $backend_form_state = SubformState::createForSubform($form['backend_config'], $form, $form_state);
       $server->getBackend()->submitConfigurationForm($form['backend_config'], $backend_form_state);
     }
 
diff --git a/src/Form/SubFormState.php b/src/Form/SubFormState.php
deleted file mode 100644
index 4509664..0000000
--- a/src/Form/SubFormState.php
+++ /dev/null
@@ -1,848 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\search_api\Form\SubFormState.
- */
-
-namespace Drupal\search_api\Form;
-
-use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\Form\FormInterface;
-use Drupal\Core\Form\FormState;
-use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Url;
-use Symfony\Component\HttpFoundation\Response;
-
-/**
- * Represents the form state of a sub-form.
- */
-class SubFormState implements FormStateInterface {
-
-  /**
-   * The keys which should be inherited as-is from the main form state.
-   *
-   * @var bool[]
-   */
-  protected static $inheritedKeys = array(
-    'build_info' => TRUE,
-    'rebuild_info' => TRUE,
-    'rebuild' => TRUE,
-    'response' => TRUE,
-    'redirect' => TRUE,
-    'redirect_route' => TRUE,
-    'no_redirect' => TRUE,
-    'method' => TRUE,
-    'cache' => TRUE,
-    'no_cache' => TRUE,
-    'triggering_element' => TRUE,
-  );
-
-  /**
-   * The form state of the main form.
-   *
-   * @var \Drupal\Core\Form\FormStateInterface
-   */
-  protected $mainFormState;
-
-  /**
-   * The keys that lead to the desired sub-form in the main form.
-   *
-   * @var string[]
-   */
-  protected $subKeys;
-
-  /**
-   * Internal storage for the sub-state, writing into the main form state.
-   *
-   * @var array
-   */
-  protected $internalStorage;
-
-  /**
-   * The values of the sub-form.
-   *
-   * @var array
-   */
-  protected $values;
-
-  /**
-   * The input of the sub-form.
-   *
-   * @var array
-   */
-  protected $input;
-
-  /**
-   * Constructs a SubFormState object.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $main_form_state
-   *   The state of the main form.
-   * @param string[] $sub_keys
-   *   The keys that lead to the desired sub-form in the main form.
-   */
-  public function __construct(FormStateInterface $main_form_state, array $sub_keys) {
-    $this->mainFormState = $main_form_state;
-    $this->subKeys = $sub_keys;
-    $sub_state = &$main_form_state->get('sub_states');
-    if (!isset($sub_state)) {
-      $sub_state = array();
-    }
-    $this->internalStorage = &$this->applySubKeys($sub_state);
-    if (!isset($this->internalStorage)) {
-      $this->internalStorage = array();
-    }
-    $this->values = &$this->applySubKeys($main_form_state->getValues());
-    if (!is_array($this->values)) {
-      $this->values = array();
-    }
-    $this->input = &$this->applySubKeys($main_form_state->getUserInput());
-    if (!is_array($this->input)) {
-      $this->input = array();
-    }
-  }
-
-  /**
-   * Applies the sub-form's array keys to the given original array.
-   *
-   * @param array $original
-   *   The original array, belonging to the main form.
-   *
-   * @return array
-   *   The corresponding array for the sub form, as a reference.
-   */
-  protected function &applySubKeys(array &$original) {
-    return NestedArray::getValue($original, $this->subKeys);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getCompleteForm() {
-    return $this->applySubKeys($this->mainFormState->getCompleteForm());
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setCompleteForm(array &$complete_form) {
-    $sub_form = &$this->applySubKeys($this->mainFormState->getCompleteForm());
-    $sub_form = $complete_form;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function loadInclude($module, $type, $name = NULL) {
-    return $this->mainFormState->loadInclude($module, $type, $name);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableArray() {
-    return array();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setFormState(array $form_state_additions) {
-    foreach ($form_state_additions as $key => $value) {
-      $this->set($key, $value);
-    }
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setResponse(Response $response) {
-    $this->mainFormState->setResponse($response);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getResponse() {
-    return $this->mainFormState->getResponse();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setRedirect($route_name, array $route_parameters = array(), array $options = array()) {
-    $this->mainFormState->setRedirect($route_name, $route_parameters, $options);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setRedirectUrl(Url $url) {
-    $this->mainFormState->setRedirectUrl($url);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRedirect() {
-    return $this->mainFormState->getRedirect();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setStorage(array $storage) {
-    $this->internalStorage = $storage;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getStorage() {
-    return $this->internalStorage;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &get($property) {
-    if (isset(self::$inheritedKeys[$property])) {
-      return $this->mainFormState->get($property);
-    }
-    $value = &NestedArray::getValue($this->internalStorage, (array) $property);
-    return $value;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function set($property, $value) {
-    if (isset(self::$inheritedKeys[$property])) {
-      $this->mainFormState->set($property, $value);
-    }
-    else {
-      $this->internalStorage[$property] = $value;
-    }
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function has($property) {
-    return isset(self::$inheritedKeys[$property])
-        || array_key_exists($property, $this->internalStorage);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setBuildInfo(array $build_info) {
-    $this->mainFormState->setBuildInfo($build_info);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getBuildInfo() {
-    return $this->mainFormState->getBuildInfo();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function addBuildInfo($property, $value) {
-    $this->mainFormState->addBuildInfo($property, $value);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getUserInput() {
-    $user_input = &$this->mainFormState->getUserInput();
-    return $this->applySubKeys($user_input);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setUserInput(array $user_input) {
-    $old = &$this->getUserInput();
-    $old = $user_input;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getValues() {
-    return $this->values;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getValue($key, $default = NULL) {
-    $exists = NULL;
-    $value = &NestedArray::getValue($this->getValues(), (array) $key, $exists);
-    if (!$exists) {
-      $value = $default;
-    }
-    return $value;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValues(array $values) {
-    $this->values = $values;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValue($key, $value) {
-    $this->values[$key] = $value;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function unsetValue($key) {
-    unset($this->values[$key]);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasValue($key) {
-    if (isset($this->values[$key])) {
-      return TRUE;
-    }
-    return FALSE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isValueEmpty($key) {
-    if (empty($this->values[$key])) {
-      return TRUE;
-    }
-    return FALSE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValueForElement(array $element, $value) {
-    $this->mainFormState->setValueForElement($element, $value);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function hasAnyErrors() {
-    return FormState::hasAnyErrors();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setErrorByName($name, $message = '') {
-    $this->mainFormState->setErrorByName(implode('][', $this->subKeys) . '][' . $name, $message);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setError(array &$element, $message = '') {
-    $this->mainFormState->setError($element, $message);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function clearErrors() {
-    $this->mainFormState->clearErrors();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getErrors() {
-    return $this->mainFormState->getErrors();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getError(array $element) {
-    return $this->mainFormState->getError($element);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setRebuild($rebuild = TRUE) {
-    $this->mainFormState->setRebuild($rebuild);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isRebuilding() {
-    return $this->mainFormState->isRebuilding();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setInvalidToken($invalid_token) {
-    $this->mainFormState->setInvalidToken($invalid_token);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasInvalidToken() {
-    return $this->mainFormState->hasInvalidToken();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function prepareCallback($callback) {
-    return $this->mainFormState->prepareCallback($callback);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getFormObject() {
-    return $this->mainFormState->getFormObject();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setFormObject(FormInterface $form_object) {
-    $this->mainFormState->setFormObject($form_object);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setAlwaysProcess($always_process = TRUE) {
-    $this->mainFormState->setAlwaysProcess($always_process);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getAlwaysProcess() {
-    return $this->mainFormState->getAlwaysProcess();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setButtons(array $buttons) {
-    $this->mainFormState->setButtons($buttons);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getButtons() {
-    return $this->mainFormState->getButtons();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setCached($cache = TRUE) {
-    $this->mainFormState->setCached($cache);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isCached() {
-    return $this->mainFormState->isCached();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function disableCache() {
-    $this->mainFormState->disableCache();
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setExecuted() {
-    $this->mainFormState->setExecuted();
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isExecuted() {
-    return $this->mainFormState->isExecuted();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  // @todo What are groups? Is this the way to handle them in a sub-form?
-  public function setGroups(array $groups) {
-    $this->mainFormState->setGroups($groups);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getGroups() {
-    return $this->mainFormState->getGroups();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setHasFileElement($has_file_element = TRUE) {
-    $this->mainFormState->setHasFileElement($has_file_element);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasFileElement() {
-    return $this->mainFormState->hasFileElement();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setLimitValidationErrors($limit_validation_errors) {
-    $add_subkeys = function(array $path) {
-      return array_merge($this->subKeys, $path);
-    };
-    $limit_validation_errors = array_map($add_subkeys, $limit_validation_errors);
-    $this->mainFormState->setLimitValidationErrors($limit_validation_errors);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getLimitValidationErrors() {
-    $limit_validation_errors = $this->mainFormState->getLimitValidationErrors();
-    if ($limit_validation_errors === NULL) {
-      return NULL;
-    }
-    $return = array();
-    $sub_keys_count = count($this->subKeys);
-    foreach ($limit_validation_errors as $path) {
-      if (array_slice($path, 0, $sub_keys_count) == $sub_keys_count) {
-        // If the whole sub-form is included, it is the same (for the sub-form)
-        // as if there was no limitation at all.
-        if (count($path) == $sub_keys_count) {
-          return NULL;
-        }
-        $return[] = $path;
-      }
-    }
-    return $return;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setMethod($method) {
-    $this->mainFormState->setMethod($method);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setRequestMethod($method) {
-    $this->mainFormState->setRequestMethod($method);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isMethodType($method_type) {
-    return $this->mainFormState->isMethodType($method_type);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValidationEnforced($must_validate = TRUE) {
-    $this->mainFormState->setValidationEnforced($must_validate);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isValidationEnforced() {
-    return $this->mainFormState->isValidationEnforced();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function disableRedirect($no_redirect = TRUE) {
-    $this->mainFormState->disableRedirect($no_redirect);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isRedirectDisabled() {
-    return $this->mainFormState->isRedirectDisabled();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setProcessInput($process_input = TRUE) {
-    $this->mainFormState->setProcessInput($process_input);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isProcessingInput() {
-    return $this->mainFormState->isProcessingInput();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setProgrammed($programmed = TRUE) {
-    $this->mainFormState->setProgrammed($programmed);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isProgrammed() {
-    return $this->mainFormState->isProgrammed();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setProgrammedBypassAccessCheck($programmed_bypass_access_check = TRUE) {
-    $this->mainFormState->setProgrammedBypassAccessCheck($programmed_bypass_access_check);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isBypassingProgrammedAccessChecks() {
-    return $this->mainFormState->isBypassingProgrammedAccessChecks();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setRebuildInfo(array $rebuild_info) {
-    $this->mainFormState->setRebuildInfo($rebuild_info);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRebuildInfo() {
-    return $this->mainFormState->getRebuildInfo();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function addRebuildInfo($property, $value) {
-    $this->mainFormState->addRebuildInfo($property, $value);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setSubmitHandlers(array $submit_handlers) {
-    $this->mainFormState->setSubmitHandlers($submit_handlers);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getSubmitHandlers() {
-    return $this->mainFormState->getSubmitHandlers();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setSubmitted() {
-    $this->mainFormState->setSubmitted();
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isSubmitted() {
-    return $this->mainFormState->isSubmitted();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setTemporary(array $temporary) {
-    $this->mainFormState->setTemporary($temporary);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getTemporary() {
-    return $this->mainFormState->getTemporary();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getTemporaryValue($key) {
-    return $this->mainFormState->getTemporaryValue($key);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setTemporaryValue($key, $value) {
-    $this->mainFormState->setTemporaryValue($key, $value);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasTemporaryValue($key) {
-    return $this->mainFormState->getTemporaryValue($key);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setTriggeringElement($triggering_element) {
-    $this->mainFormState->setTriggeringElement($triggering_element);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function &getTriggeringElement() {
-    return $this->mainFormState->getTriggeringElement();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValidateHandlers(array $validate_handlers) {
-    $this->mainFormState->setValidateHandlers($validate_handlers);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getValidateHandlers() {
-    return $this->mainFormState->getValidateHandlers();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValidationComplete($validation_complete = TRUE) {
-    $this->mainFormState->setValidationComplete($validation_complete);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isValidationComplete() {
-    return $this->mainFormState->isValidationComplete();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getCleanValueKeys() {
-    return $this->mainFormState->getCleanValueKeys();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setCleanValueKeys(array $keys) {
-    $this->mainFormState->setCleanValueKeys($keys);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function addCleanValueKey($key) {
-    $this->mainFormState->addCleanValueKey($key);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function cleanValues() {
-    $this->mainFormState->cleanValues();
-    return $this;
-  }
-
-}