diff --git a/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/Property/TermDeltaEntityProcessorProperty.php b/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/Property/TermDeltaEntityProcessorProperty.php
new file mode 100644
index 00000000..ed4a2d27
--- /dev/null
+++ b/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/Property/TermDeltaEntityProcessorProperty.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace Drupal\materio_sapi\Plugin\search_api\processor\Property;
+
+use Drupal\Core\Entity\TypedData\EntityDataDefinition;
+use Drupal\search_api\Processor\ProcessorPropertyInterface;
+
+/**
+ * Provides a definition for a processor property that contains an entity.
+ */
+class TermDeltaEntityProcessorProperty extends EntityDataDefinition implements ProcessorPropertyInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getProcessorId() {
+    return $this->definition['processor_id'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isHidden() {
+    return !empty($this->definition['hidden']);
+  }
+
+}
diff --git a/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/TermDelta.php b/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/TermDelta.php
new file mode 100644
index 00000000..4f40da24
--- /dev/null
+++ b/web/modules/custom/materio_sapi/src/Plugin/search_api/processor/TermDelta.php
@@ -0,0 +1,430 @@
+<?php
+
+namespace Drupal\materio_sapi\Plugin\search_api\processor;
+
+use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Entity\ContentEntityTypeInterface;
+use Drupal\Core\Entity\EntityFieldManager;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\search_api\Datasource\DatasourceInterface;
+use Drupal\search_api\IndexInterface;
+use Drupal\search_api\Item\ItemInterface;
+use Drupal\search_api\Processor\EntityProcessorProperty;
+use Drupal\search_api\Processor\ProcessorPluginBase;
+use Drupal\search_api\SearchApiException;
+use Drupal\search_api\Utility\Utility;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Allows indexing of reverse entity references.
+ *
+ * @SearchApiProcessor(
+ *   id = "term_delta",
+ *   label = @Translation("Term Delta"),
+ *   description = @Translation("Allow to boost term reference field value regarding delta."),
+ *   stages = {
+ *     "add_properties" = 0,
+ *   },
+ * )
+ */
+class TermDelta extends ProcessorPluginBase {
+
+  /**
+   * Static cache for all entity references.
+   *
+   * @var array[][]|null
+   *
+   * @see \Drupal\search_api\Plugin\search_api\processor\ReverseEntityReferences::getEntityReferences()
+   */
+  protected $references;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface|null
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The entity field manager.
+   *
+   * @var \Drupal\Core\Entity\EntityFieldManager|null
+   */
+  protected $entityFieldManager;
+
+  /**
+   * The entity type bundle info.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface|null
+   */
+  protected $entityTypeBundleInfo;
+
+  /**
+   * The language manager.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface|null
+   */
+  protected $languageManager;
+
+  /**
+   * The cache.
+   *
+   * @var \Drupal\Core\Cache\CacheBackendInterface|null
+   */
+  protected $cache;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    /** @var static $processor */
+    $processor = parent::create($container, $configuration, $plugin_id, $plugin_definition);
+
+    $processor->setEntityTypeManager($container->get('entity_type.manager'));
+    $processor->setEntityFieldManager($container->get('entity_field.manager'));
+    $processor->setEntityTypeBundleInfo($container->get('entity_type.bundle.info'));
+    $processor->setLanguageManager($container->get('language_manager'));
+    $processor->setCache($container->get('cache.default'));
+
+    return $processor;
+  }
+
+  /**
+   * Retrieves the entity type manager.
+   *
+   * @return \Drupal\Core\Entity\EntityTypeManagerInterface
+   *   The entity type manager.
+   */
+  public function getEntityTypeManager() {
+    return $this->entityTypeManager ?: \Drupal::entityTypeManager();
+  }
+
+  /**
+   * Sets the entity type manager.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The new entity type manager.
+   *
+   * @return $this
+   */
+  public function setEntityTypeManager(EntityTypeManagerInterface $entity_type_manager) {
+    $this->entityTypeManager = $entity_type_manager;
+    return $this;
+  }
+
+  /**
+   * Retrieves the entity field manager.
+   *
+   * @return \Drupal\Core\Entity\EntityFieldManager
+   *   The entity field manager.
+   */
+  public function getEntityFieldManager() {
+    return $this->entityFieldManager ?: \Drupal::service('entity_field.manager');
+  }
+
+  /**
+   * Sets the entity field manager.
+   *
+   * @param \Drupal\Core\Entity\EntityFieldManager $entity_field_manager
+   *   The new entity field manager.
+   *
+   * @return $this
+   */
+  public function setEntityFieldManager(EntityFieldManager $entity_field_manager) {
+    $this->entityFieldManager = $entity_field_manager;
+    return $this;
+  }
+
+  /**
+   * Retrieves the entity type bundle info.
+   *
+   * @return \Drupal\Core\Entity\EntityTypeBundleInfoInterface
+   *   The entity type bundle info.
+   */
+  public function getEntityTypeBundleInfo() {
+    return $this->entityTypeBundleInfo ?: \Drupal::service('entity_type.bundle.info');
+  }
+
+  /**
+   * Sets the entity type bundle info.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
+   *   The new entity type bundle info.
+   *
+   * @return $this
+   */
+  public function setEntityTypeBundleInfo(EntityTypeBundleInfoInterface $entity_type_bundle_info) {
+    $this->entityTypeBundleInfo = $entity_type_bundle_info;
+    return $this;
+  }
+
+  /**
+   * Retrieves the language manager.
+   *
+   * @return \Drupal\Core\Language\LanguageManagerInterface
+   *   The language manager.
+   */
+  public function getLanguageManager() {
+    return $this->languageManager ?: \Drupal::service('language_manager');
+  }
+
+  /**
+   * Sets the language manager.
+   *
+   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
+   *   The new language manager.
+   *
+   * @return $this
+   */
+  public function setLanguageManager(LanguageManagerInterface $language_manager) {
+    $this->languageManager = $language_manager;
+    return $this;
+  }
+
+  /**
+   * Retrieves the cache.
+   *
+   * @return \Drupal\Core\Cache\CacheBackendInterface
+   *   The cache.
+   */
+  public function getCache() {
+    return $this->cache ?: \Drupal::service('cache.default');
+  }
+
+  /**
+   * Sets the cache.
+   *
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *   The new cache.
+   *
+   * @return $this
+   */
+  public function setCache(CacheBackendInterface $cache) {
+    $this->cache = $cache;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function supportsIndex(IndexInterface $index) {
+    foreach ($index->getDatasources() as $datasource) {
+      if ($datasource->getEntityTypeId()) {
+        return TRUE;
+      }
+    }
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPropertyDefinitions(DatasourceInterface $datasource = NULL) {
+    // ksm($datasource);
+    $properties = [];
+
+    if (!$datasource || !$datasource->getEntityTypeId()) {
+      return $properties;
+    }
+
+    $references = $this->getEntityReferences();
+    // ksm($references);
+
+    // $entity_type_id = $datasource->getEntityTypeId();
+    // dsm($entity_type_id);
+    if (isset($references['taxonomy_term'])) {
+      foreach ($references['taxonomy_term'] as $key => $reference) {
+        $entity_type_id = $reference['entity_type'];
+        try {
+          $entity_type = $this->getEntityTypeManager()
+            ->getDefinition($entity_type_id);
+        }
+        catch (PluginNotFoundException $e) {
+          continue;
+        }
+        // ksm($entity_type);
+
+        for ($delta=0; $delta < 5; $delta++) {
+          $args = [
+            '@delta' => $delta,
+            '@entity_type' => $entity_type->getLabel(),
+            '@property' => $reference['label'],
+          ];
+          $definition = [
+            'label' => $this->t('@property [@delta] on @entity_type', $args),
+            // 'description' => $this->t("All %entity_type entities that reference this item via the %property field."),
+            'description' => $this->t("Term Delta [@delta] from field @property on @entity_type.", $args),
+            'type' => "entity:taxonomy_term",
+            'processor_id' => $this->getPluginId(),
+            // We can't really know whether this will end up being multi-valued, so
+            // we err on the side of caution.
+            'is_list' => TRUE,
+          ];
+          $property = new EntityProcessorProperty($definition);
+          $property->setEntityTypeId('taxonomy_term');
+          $properties["materio_sapi_term_delta__{$entity_type_id}__{$reference['label']}__{$delta}"] = $property;
+          // code...
+        }
+      }
+    }
+
+    return $properties;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addFieldValues(ItemInterface $item) {
+    // get the original indexed entity
+    try {
+      $entity = $item->getOriginalObject()->getValue();
+    }
+    catch (SearchApiException $e) {
+      return;
+    }
+
+    if (!($entity instanceof EntityInterface)) {
+      return;
+    }
+    // get the original
+    $entity_type_id = $entity->getEntityTypeId();
+    $entity_id = $entity->id();
+    $langcode = $entity->language()->getId();
+    $datasource_id = $item->getDatasourceId();
+
+    /** @var \Drupal\search_api\Item\FieldInterface[][][] $to_extract */
+    $to_extract = [];
+    $prefix = 'materio_sapi_term_delta__';
+    $prefix_length = strlen($prefix);
+    foreach ($item->getFields() as $field) {
+      $property_path = $field->getPropertyPath();
+      list($direct, $nested) = Utility::splitPropertyPath($property_path, FALSE);
+      if ($field->getDatasourceId() === $datasource_id
+          && substr($direct, 0, $prefix_length) === $prefix) {
+        $property_name = substr($direct, $prefix_length);
+        $to_extract[$property_name][$nested][] = $field;
+      }
+    }
+    // ksm($to_extract);
+    $references = $this->getEntityReferences();
+    foreach ($to_extract as $property_name => $fields_to_extract) {
+      if (!isset($references[$entity_type_id][$property_name])) {
+        continue;
+      }
+      $property_info = $references[$entity_type_id][$property_name];
+
+      try {
+        $storage = $this->getEntityTypeManager()
+          ->getStorage($property_info['entity_type']);
+      }
+      // @todo Replace with multi-catch once we depend on PHP 7.1+.
+      catch (InvalidPluginDefinitionException $e) {
+        continue;
+      }
+      catch (PluginNotFoundException $e) {
+        continue;
+      }
+      $entity_ids = $storage->getQuery()
+        ->accessCheck(FALSE)
+        ->condition($property_info['property'], $entity_id)
+        ->execute();
+
+      $entities = $storage->loadMultiple($entity_ids);
+      if (!$entities) {
+        continue;
+      }
+
+      // This is a pretty hack-y work-around to make property extraction work for
+      // Views fields, too. In general, adding entities as field values is a
+      // pretty bad idea, so this might blow up in some use cases. Just do it for
+      // now and hope for the best.
+      if (isset($fields_to_extract[''])) {
+        foreach ($fields_to_extract[''] as $field) {
+          $field->setValues(array_values($entities));
+        }
+        unset($fields_to_extract['']);
+      }
+      foreach ($entities as $referencing_entity) {
+        $typed_data = $referencing_entity->getTypedData();
+        $this->getFieldsHelper()
+          ->extractFields($typed_data, $fields_to_extract, $langcode);
+      }
+    }
+  }
+
+  /**
+   * Collects all entity references.
+   *
+   * @return array[][]
+   *   An associative array of entity reference information keyed by the
+   *   referenced entity type's ID and a custom identifier for the property
+   *   (consisting of referencing entity type and property name), with values
+   *   being associative arrays with the following keys:
+   *   - label: The property label.
+   *   - entity_type: The referencing entity type.
+   *   - property: The property name.
+   */
+  public function getEntityReferences() {
+    if ($this->references !== NULL) {
+      return $this->references;
+    }
+
+    // Property labels differ by language, so we need to vary the cache
+    // according to the current language.
+    $langcode = $this->getLanguageManager()->getCurrentLanguage()->getId();
+    $cid = "search_api:term_delta:$langcode";
+    $cache = $this->getCache()->get($cid);
+    if (isset($cache->data)) {
+      $this->references = $cache->data;
+    }
+    else {
+      $this->references = [];
+
+      $entity_types = $this->getEntityTypeManager()->getDefinitions();
+      $field_manager = $this->getEntityFieldManager();
+      $entity_type_bundle_info = $this->getEntityTypeBundleInfo();
+      foreach ($entity_types as $entity_type_id => $entity_type) {
+        if (!($entity_type instanceof ContentEntityTypeInterface)) {
+          continue;
+        }
+        /** @var \Drupal\Core\Field\FieldDefinitionInterface[] $properties */
+        $properties = $field_manager->getBaseFieldDefinitions($entity_type_id);
+        $bundles = $entity_type_bundle_info->getBundleInfo($entity_type_id);
+        foreach ($bundles as $bundle => $info) {
+          $properties += $field_manager->getFieldDefinitions($entity_type_id, $bundle);
+        }
+
+        foreach ($properties as $name => $property) {
+          if ($property->getType() !== 'entity_reference') {
+            continue;
+          }
+          $settings = $property->getSettings();
+          if (empty($settings['target_type'])) {
+            continue;
+          }
+          $this->references[$settings['target_type']]["{$entity_type_id}__$name"] = [
+            'label' => $property->getLabel(),
+            'entity_type' => $entity_type_id,
+            'property' => $name,
+          ];
+        }
+      }
+
+      $tags = [
+        'entity_types',
+        'entity_bundles',
+        'entity_field_info',
+      ];
+      $this->getCache()->set($cid, $this->references, Cache::PERMANENT, $tags);
+    }
+
+    return $this->references;
+  }
+
+}