diff --git a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
index 2d58dd1..76cd23a 100644
--- a/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
+++ b/core/lib/Drupal/Core/Entity/RevisionableSchemaConverter.php
@@ -35,6 +35,7 @@ class RevisionableSchemaConverter implements RevisionableSchemaConverterInterfac
 
   /**
    * EntitySchemaUpdater constructor.
+   *
    * @param \Drupal\Core\Entity\EntityLastInstalledSchemaRepositoryInterface $last_installed_schema_repository
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
    * @param \Drupal\Core\Entity\EntityDefinitionUpdateManagerInterface $entity_definition_update_manager
@@ -62,6 +63,7 @@ public function convertSchema(EntityTypeInterface $entity_type) {
    * {@inheritdoc}
    */
   public function copyData(EntityTypeInterface $entity_type, array &$sandbox) {
+    // If 'progress' is not set, then this will be the first run of the batch.
     if (!isset($sandbox['progress'])) {
       $base_table = $entity_type->getBaseTable();
       $sandbox['progress'] = 0;
@@ -79,8 +81,10 @@ public function copyData(EntityTypeInterface $entity_type, array &$sandbox) {
     $revision_id = $entity_type->getKey('revision');
 
     $data = [];
+    // Loop through all tables for the entity type and combine the data.
     foreach ($table_names as $table_name) {
       $column_names = $table_mapping->getAllColumns($table_name);
+      // Process 5 entities per batch.
       $results = $this->database->select($table_name, 't')
         ->fields('t')
         ->condition($id, $sandbox['current_id'], '>')
@@ -97,6 +101,7 @@ public function copyData(EntityTypeInterface $entity_type, array &$sandbox) {
       }
     }
 
+    // Loop through all the collected data and update / insert missing rows.
     foreach ($data as $record) {
       if (!empty($record[$id])) {
         $record[$revision_id] = $record[$id];
@@ -175,7 +180,6 @@ protected function installFields(EntityTypeInterface $entity_type) {
         ->setSetting('unsigned', TRUE);
       $this->entityDefinitionUpdateManager
         ->installFieldStorageDefinition($entity_type->getKey('revision'), $entity_type->id(), $entity_type->id(), $revision_id);
-
     }
 
     $revision_created = BaseFieldDefinition::create('created')