diff --git a/src/Form/MigrateUpgradeForm.php b/src/Form/MigrateUpgradeForm.php
index 72f1092..416886c 100644
--- a/src/Form/MigrateUpgradeForm.php
+++ b/src/Form/MigrateUpgradeForm.php
@@ -39,9 +39,9 @@ class MigrateUpgradeForm extends ConfirmFormBase {
   /**
    * Mapping of known migrations and their source and destination modules.
    *
-   * @todo Hardcoding this information is not robust - the migrations
-   *   themselves should hold the necessary information.
-   * @see https://www.drupal.org/node/2569805
+   * @todo https://www.drupal.org/node/2569805 Hardcoding this information is
+   *   not robust - the migrations themselves should hold the necessary
+   *   information.
    *
    * @var array[]
    */
@@ -597,21 +597,29 @@ class MigrateUpgradeForm extends ConfirmFormBase {
   ];
 
   /**
+   * The state service.
+   *
    * @var \Drupal\Core\State\StateInterface
    */
   protected $state;
 
   /**
+   * The date formatter service.
+   *
    * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
   /**
+   * The renderer service.
+   *
    * @var \Drupal\Core\Render\RendererInterface
    */
   protected $renderer;
 
   /**
+   * The migration entity storage.
+   *
    * @var \Drupal\Core\Entity\EntityStorageInterface
    */
   protected $entityStorage;
@@ -620,9 +628,13 @@ class MigrateUpgradeForm extends ConfirmFormBase {
    * MigrateUpgradeForm constructor.
    *
    * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
    * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
+   *   The date formatter service.
    * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer service.
    * @param \Drupal\Core\Entity\EntityStorageInterface $entity_storage
+   *   The migration entity storage.
    */
   public function __construct(StateInterface $state, DateFormatterInterface $date_formatter, RendererInterface $renderer, EntityStorageInterface $entity_storage) {
     $this->state = $state;
@@ -786,6 +798,9 @@ class MigrateUpgradeForm extends ConfirmFormBase {
    *
    * @return array
    *   The form structure.
+   *
+   * @todo Private files directory not yet implemented, depends on
+   *   https://www.drupal.org/node/2547125.
    */
   public function buildCredentialForm(array $form, FormStateInterface $form_state) {
     $form['#title'] = $this->t('Drupal Upgrade');
@@ -860,15 +875,6 @@ class MigrateUpgradeForm extends ConfirmFormBase {
       '#description' => $this->t('To import files from your current Drupal site, enter a local file directory containing your site (e.g. /var/www/docroot), or your site address (e.g. http://example.com).'),
     ];
 
-    /*
-    // @todo Not yet implemented, depends on https://www.drupal.org/node/2547125.
-    $form['files']['private_file_directory'] = [
-      '#type' => 'textfield',
-      '#title' => $this->t('Private file path'),
-      '#description' => $this->t('To import private files from your current Drupal site, enter a local file directory containing your files (e.g. /var/private_files).'),
-    ];
-     */
-
     $form['actions'] = ['#type' => 'actions'];
     $form['actions']['save'] = [
       '#type' => 'submit',
@@ -1085,7 +1091,7 @@ class MigrateUpgradeForm extends ConfirmFormBase {
         foreach ($destination_module_info as $destination_module => $migration_ids) {
           $destination_details[$destination_module] = [
             '#type' => 'item',
-            '#plain_text' => $this->t($destination_module),
+            '#plain_text' => $destination_module,
           ];
         }
         $form['available_module_list']['module_list'][$source_module] = [
diff --git a/src/MigrateMessageCapture.php b/src/MigrateMessageCapture.php
index 3ccef90..cb5fdcd 100644
--- a/src/MigrateMessageCapture.php
+++ b/src/MigrateMessageCapture.php
@@ -39,6 +39,7 @@ class MigrateMessageCapture implements MigrateMessageInterface {
    * Returns any captured messages.
    *
    * @return array
+   *   The captured messages.
    */
   public function getMessages() {
     return $this->messages;
diff --git a/src/MigrateUpgradeRunBatch.php b/src/MigrateUpgradeRunBatch.php
index 72dfdc1..5809176 100644
--- a/src/MigrateUpgradeRunBatch.php
+++ b/src/MigrateUpgradeRunBatch.php
@@ -19,6 +19,9 @@ use Drupal\migrate\Event\MigratePostRowSaveEvent;
 use Drupal\migrate\Event\MigrateRowDeleteEvent;
 use Drupal\migrate\MigrateExecutable;
 
+/**
+ * Runs a single migration batch.
+ */
 class MigrateUpgradeRunBatch {
 
   /**
@@ -60,7 +63,7 @@ class MigrateUpgradeRunBatch {
    * @param int[] $initial_ids
    *   The full set of migration IDs to import.
    * @param string $operation
-   *   'import' or 'rollback'.
+   *   The operation to perform, 'import' or 'rollback'.
    * @param array $context
    *   The batch context.
    */
@@ -111,7 +114,7 @@ class MigrateUpgradeRunBatch {
 
       $migration_name = $migration->label() ? $migration->label() : $migration_id;
 
-      try  {
+      try {
         if ($operation == 'import') {
           $migration_status = $executable->import();
         }
@@ -188,7 +191,7 @@ class MigrateUpgradeRunBatch {
       $message_count = count($context['sandbox']['messages']);
       $context['message'] = '';
       for ($index = max(0, $message_count - self::MESSAGE_LENGTH); $index < $message_count; $index++) {
-        $context['message'] = $context['sandbox']['messages'][$index]. "<br />\n" . $context['message'];
+        $context['message'] = $context['sandbox']['messages'][$index] . "<br />\n" . $context['message'];
       }
       if ($message_count > self::MESSAGE_LENGTH) {
         // Indicate there are earlier messages not displayed.
@@ -284,8 +287,8 @@ class MigrateUpgradeRunBatch {
     }
     else {
       if ($results['operation'] == 'import') {
-        // Everything went off without a hitch. We may not have had successes but
-        // we didn't have failures so this is fine.
+        // Everything went off without a hitch. We may not have had successes
+        // but we didn't have failures so this is fine.
         drupal_set_message(t('Congratulations, you upgraded Drupal!'));
       }
       else {
diff --git a/src/MigrationCreationTrait.php b/src/MigrationCreationTrait.php
index 98a56da..3845449 100644
--- a/src/MigrationCreationTrait.php
+++ b/src/MigrationCreationTrait.php
@@ -20,12 +20,13 @@ use Drupal\Component\Plugin\Exception\PluginNotFoundException;
 trait MigrationCreationTrait {
 
   /**
-   * Get the database connection for the source Drupal database.
+   * Gets the database connection for the source Drupal database.
    *
    * @param array $database
    *   Database array representing the source Drupal database.
    *
    * @return \Drupal\Core\Database\Connection
+   *   The database connection for the source Drupal database.
    */
   protected function getConnection(array $database) {
     // Set up the connection.
@@ -35,19 +36,20 @@ trait MigrationCreationTrait {
   }
 
   /**
-   * Get the system data from the system table of the source Drupal database.
+   * Gets the system data from the system table of the source Drupal database.
    *
    * @param array $database
    *   Database array representing the source Drupal database.
    *
    * @return array
+   *   The system data from the system table of the source Drupal database.
    */
   protected function getSystemData(array $database) {
     $connection = $this->getConnection($database);
     $system_data = [];
     try {
       $results = $connection->select('system', 's', [
-        'fetch' => \PDO::FETCH_ASSOC
+        'fetch' => \PDO::FETCH_ASSOC,
       ])
         ->fields('s')
         ->execute();
@@ -104,12 +106,16 @@ trait MigrationCreationTrait {
   }
 
   /**
-   * Gets the relevant migrations for import from the provided migration template connection.
+   * Gets the migrations for import.
+   *
+   * Uses the migration template connection to ensure that only the relevant
+   * migrations are returned.
    *
    * @param array $migration_templates
    *   Migration template.
    *
    * @return \Drupal\migrate\Entity\MigrationInterface[]
+   *   The migrations for import.
    */
   protected function getMigrations(array $migration_templates) {
     // Let the builder service create our migration configuration entities from
@@ -143,13 +149,13 @@ trait MigrationCreationTrait {
   }
 
   /**
-   * Saves the relevant migrations for import from the provided template
-   * connection.
+   * Saves the migrations for import from the provided template connection.
    *
    * @param array $migration_templates
    *   Migration template.
    *
    * @return array
+   *   The migration IDs sorted in dependency order.
    */
   protected function createMigrations(array $migration_templates) {
     $migration_ids = [];