diff --git a/src/Form/IndexAddFieldsForm.php b/src/Form/IndexAddFieldsForm.php
index b534aac..9d76f8b 100644
--- a/src/Form/IndexAddFieldsForm.php
+++ b/src/Form/IndexAddFieldsForm.php
@@ -7,7 +7,6 @@
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\Datetime\DateFormatter;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Entity\TypedData\EntityDataDefinitionInterface;
@@ -16,7 +15,6 @@
 use Drupal\Core\TypedData\ComplexDataDefinitionInterface;
 use Drupal\Core\TypedData\DataReferenceDefinitionInterface;
 use Drupal\Core\Url;
-use Drupal\search_api\Datasource\DatasourceInterface;
 use Drupal\search_api\Processor\ConfigurablePropertyInterface;
 use Drupal\search_api\Processor\ProcessorPropertyInterface;
 use Drupal\search_api\Utility\FieldsHelperInterface;
@@ -62,15 +60,6 @@ class IndexAddFieldsForm extends EntityForm {
   protected $unmappedFields = array();
 
   /**
-   * REMOVE.
-   *
-   * Counter keeping track of the sequence of method invocation.
-   *
-   * @var int
-   */
-  protected static $sequenceCounter = 0;
-
-  /**
    * {@inheritdoc}
    */
   public function getFormId() {
@@ -104,8 +93,6 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager, Fie
     $this->renderer = $renderer;
     $this->dateFormatter = $date_formatter;
     $this->parameters = $parameters;
-    // REMOVE.
-    $this->displayMethodInvocation('__construct');
   }
 
   /**
@@ -122,7 +109,6 @@ public static function create(ContainerInterface $container) {
     return new static($entity_type_manager, $fields_helper, $renderer, $date_formatter, $parameters);
   }
 
-
   /**
    * Retrieves a single page request parameter.
    *
@@ -142,9 +128,6 @@ public function getParameter($name, $default = NULL) {
    * {@inheritdoc}
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
-
-    $this->displayMethodInvocation('buildForm');
-
     $index = $this->entity;
 
     // Do not allow the form to be cached. See
@@ -153,7 +136,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
 
     $this->checkEntityEditable($form, $index);
 
-    // Set title. Strip html to accomodate modal title.
+    // Set title. Strip html to accommodate modal title.
     $args['%index'] = $index->label();
     $form['#title'] = PlainTextOutput::renderFromHtml($this->t('Add fields to index %index', $args));
 
@@ -163,27 +146,16 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#attributes' => ['id' => 'index-fields'],
     ];
 
-    // TEST.
-    $form['index-fields']['messages'] = [
-      '#type' => 'container',
-      '#attributes' => ['id' => 'message-wrapper'],
-    ];
-
-    // We store the datasources we need to show in the form
-    // to accomodate the ajax magic.
+    // We store the datasources we need to show in the form to accommodate the
+    // AJAX magic.
     // Create hidden form field to store datasources.
     $form['datasources'] = array(
       '#type' => 'hidden',
     );
 
+    $datasources = $form_state->getValue('datasources');
     // First set some defaults when nothing is set.
-    $form_state_datasources = $form_state->getValue('datasources');
-
-    dsm('form state at start of build form');
-    dsm($form_state_datasources);
-
-    if (empty($form_state_datasources)) {
-      dsm('leeg dus invullen');
+    if (empty($datasources)) {
       // Get the datasources to add.
       // Start with the general fields.
       $datasources = ['general' => NULL];
@@ -194,16 +166,10 @@ public function buildForm(array $form, FormStateInterface $form_state) {
         $datasource_id = $entity_datasource->getPluginId();
         $datasources[$datasource_id] = NULL;
       }
-      $form['datasources']['#value'] = $datasources;
-    }
-    else {
-      dsm('niet leeg');
-      $form['datasources']['#value'] = $form_state_datasources;
     }
-    dsm('deze datasources moeten we weergeven');
-    dsm($form['datasources']['#value']);
+    $form['datasources']['#value'] = $datasources;
 
-    // Create form elementes for each of the datasources we want to show.
+    // Create form elements for each of the datasources we want to show.
     // This is a recursive function, allowing to show the nested elements.
     $containers = $this->createFieldContainers($form['datasources']['#value']);
     $form['index-fields']['properties'] = $containers;
@@ -237,96 +203,61 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   }
 
   /**
-   * Create form elements for each field.
+   * Creates form elements for each field.
    *
    * @param array $fields
    *   A nested array which defines what fields to show. This info is
    *   stored in the form.
    *
    * @return array
-   *   Return form elements.
+   *   Form elements for the given fields..
    */
   protected function createFieldContainers(array $fields) {
-    foreach (array_keys($fields) as $datasource_id) {
+    $items = array();
+    $url = $this->entity->toUrl('add-fields');
 
-      // Each element get's a container so we can add children for subelements.
-      $item = array(
+    foreach (array_keys($fields) as $datasource_id) {
+      // Each element get' a container so we can add children for sub elements.
+      $item = [
         '#type' => 'container',
-        '#attributes' => array(
-          'class' => array('container-inline'),
+        '#attributes' => [
+          'class' => ['container-inline'],
           '#attributes' => ['id' => '' . $datasource_id],
-        ),
+        ],
         '#field-name' => $datasource_id,
-      );
+      ];
 
-      $item['test'] = array(
+      $item['test'] = [
         '#markup' => 'Show ' . $datasource_id . ' in ' . 'index-field-' . $datasource_id . ' container',
-      );
+      ];
 
       $active = FALSE;
-
       $active_datasource = $this->getParameter('datasource');
       if (isset($active_datasource)) {
         $active = $active_datasource == $datasource_id;
       }
 
-      $url = $this->entity->toUrl('add-fields');
-      if ($active) {
-        $expand_link = array(
-          '#type' => 'link',
-          '#title' => '(-) ',
-          '#url' => $url,
-        );
-      }
-      else {
-        $url->setOption('query', array('datasource' => $datasource_id));
-        $expand_link = array(
-          '#type' => 'link',
-          '#title' => '(+) ',
-          '#url' => $url,
-        );
-        $expand_button = array(
-          '#type' => 'submit',
-          '#name' => 'expand_datasource_' . $datasource_id,
-          '#value' => '(+)',
-          '#submit' => ['::expandDatasourceFormSubmit'],
-          '#ajax' => [
-            'callback' => '::expandDatasourceFormAjax',
-            'wrapper' => 'index-fields',
-            'effect' => 'fade',
-            'method' => 'replace',
-          ],
-        );
-
-      }
-      $item['expand_link'] = $expand_link;
-      $item['expand_button'] = $expand_button;
-
-      //$label = $fields[$datasource_id] ? $fields[$datasource_id] : $this->t('General');
-      //$item['label']['#markup'] = $label;
-
-      if ($active) {
-        $properties = $this->entity->getPropertyDefinitions($datasource_id == 'general' ? NULL: $datasource_id);
-        if ($properties) {
+      $properties = $this->entity->getPropertyDefinitions($datasource_id == 'general' ? NULL : $datasource_id);
+      if ($properties) {
+        $active_property_path = NULL;
+        if ($active) {
           $active_property_path = $this->getParameter('property_path', '');
-          $base_url = clone $url;
-          $base_url->setOption('query', array('datasource' => $datasource_id));
-          $item['properties'] = $this->getPropertiesList($properties, $active_property_path, $base_url);
         }
+        $base_url = clone $url;
+        $base_url->setOption('query', array('datasource' => $datasource_id));
+        $item['properties'] = $this->getPropertiesList($properties, $active_property_path, $base_url);
       }
       $items[] = $item;
 
       // Add child elements.
-      if(is_array($fields[$datasource_id])){
-        // Add new things.
+      if (is_array($fields[$datasource_id])) {
         $new_things = $this->createFieldContainers($fields[$datasource_id]);
-        foreach($new_things as $new_thing){
+        foreach ($new_things as $new_thing) {
           $items[] = $new_thing;
         }
       }
-
-
     }
+
     return $items;
   }
 
@@ -334,9 +265,6 @@ protected function createFieldContainers(array $fields) {
    * Handles form submissions for expanding a datasource.
    */
   public function expandDatasourceFormSubmit(&$form, FormStateInterface &$form_state) {
-    // REMOVE.
-    $this->displayMethodInvocation('expandDatasourceFormSubmit');
-
     // Find the triggering field.
     $button = $form_state->getTriggeringElement();
     // Go one level up in the form, to the widgets container.
@@ -348,86 +276,22 @@ public function expandDatasourceFormSubmit(&$form, FormStateInterface &$form_sta
 
     $properties = $this->entity->getPropertyDefinitions($field_name == 'general' ? NULL : $field_name);
 
-    //dsm(array_keys($properties));
-    dsm('opgevraagde datasources');
-    dsm($datasources);
-    foreach(array_keys($properties) as $property){
+    foreach (array_keys($properties) as $property) {
       $datasources[$field_name][$property] = NULL;
     }
 
-    dsm('datasources changes uit ajax submit');
-    dsm($datasources);
     $form_state->setValue('datasources', $datasources);
-    dsm('opgeslaan in datasources?');
-      dsm($form_state->getValue('datasources'));
     $form_state->setRebuild();
   }
 
   /**
-   * Return new datasource structure.
+   * Returns new datasource structure.
    */
   public function expandDatasourceFormAjax(array $form, FormStateInterface &$form_state) {
-
-
-    $this->displayMethodInvocation('expandDatasourceFormAjax');
-    //dsm($form_state->getValue('datasource'));
-    //$form = $form_state->getCompleteForm();
-    //$button = $form_state->getTriggeringElement();
-
-    // Go one level up in the form, to the widgets container.
-    //dsm('array of button parrents');
-    //dsm($button['#array_parents']);
-    //$element = NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -3));
-    //echo 'Which element trigggered?';
-    //dsm('Which element trigggered?');
-
-    //dsm(array_keys($element));
-    //dsm($element['#type']);
-    //dsm($element['field-name']);
-
     $form['messages']['status'] = [
       '#type' => 'status_messages',
     ];
-//dsm($form['datasources']['#value']);
-
-    //$datasources = $form_state->getValue('datasources');
-    //dsm($datasources);
-    //$form['datasources']['#value'] = $datasources;
-    //return $form['messages'];
-    //return $form['index-fields'];
-    //return $element;
     return $form;
-
-    /*
-     * $button = $form_state->getTriggeringElement();
-
-
-    // Ensure the widget allows adding additional items.
-    if ($element['#cardinality'] != FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED) {
-      return;
-    }
-
-    // Add a DIV around the delta receiving the Ajax effect.
-    $delta = $element['#max_delta'];
-    $element[$delta]['#prefix'] = '<div class="ajax-new-content">' . (isset($element[$delta]['#prefix']) ? $element[$delta]['#prefix'] : '');
-    $element[$delta]['#suffix'] = (isset($element[$delta]['#suffix']) ? $element[$delta]['#suffix'] : '') . '</div>';
-
-    return $element;
-     */
-  }
-
-  /**
-   * Update form processing information.
-   *
-   * Display the method being called and it's sequence in the form
-   * processing.
-   *
-   * @param string $method_name
-   *   The method being invoked.
-   */
-  private function displayMethodInvocation($method_name) {
-    self::$sequenceCounter++;
-    drupal_set_message(self::$sequenceCounter . ". $method_name");
   }
 
   /**
@@ -450,7 +314,6 @@ private function displayMethodInvocation($method_name) {
    *   properties.
    */
   protected function getPropertiesList(array $properties, $active_property_path, Url $base_url, $parent_path = '', $label_prefix = '') {
-
     $list = array(
       '#theme' => 'search_api_form_item_list',
     );
@@ -523,8 +386,8 @@ protected function getPropertiesList(array $properties, $active_property_path, U
         continue;
       }
 
-      $nested_list = array();
-      $expand_link = array();
+      $nested_list = FALSE;
+      $expand_link = FALSE;
       if ($nested_properties) {
         if ($key == $active_item) {
           $link_url = clone $base_url;
@@ -534,6 +397,11 @@ protected function getPropertiesList(array $properties, $active_property_path, U
             '#type' => 'link',
             '#title' => '(-) ',
             '#url' => $link_url,
+            '#attributes' => [
+              'class' => [
+                'use-ajax',
+              ],
+            ],
           );
 
           $nested_list = $this->getPropertiesList($nested_properties, $active_property_path, $base_url, $this_path, $label_prefix . $label . ' » ');
@@ -546,16 +414,10 @@ protected function getPropertiesList(array $properties, $active_property_path, U
             '#type' => 'link',
             '#title' => '(+) ',
             '#url' => $link_url,
-          );
-          $expand_button = array(
-            '#type' => 'button',
-            '#name' => 'widget_configure',
-            '#value' => '(+)',
-            '#limit_validation_errors' => [['widget']],
-            '#submit' => ['::submitAjaxWidgetConfigForm'],
-            '#ajax' => [
-              'callback' => '::buildAjaxWidgetConfigForm',
-              'wrapper' => 'index-field-list',
+            '#attributes' => [
+              'class' => [
+                'use-ajax',
+              ],
             ],
           );
         }
@@ -571,9 +433,6 @@ protected function getPropertiesList(array $properties, $active_property_path, U
       if ($expand_link) {
         $item['expand_link'] = $expand_link;
       }
-      if ($expand_button) {
-        $item['expand_button'] = $expand_button;
-      }
 
       $item['label']['#markup'] = Html::escape($label) . ' ';