diff --git a/core/modules/migrate_drupal/src/MigrationCreationTrait.php b/core/modules/migrate_drupal/src/MigrationCreationTrait.php
index 412ed09..fa08e4b 100644
--- a/core/modules/migrate_drupal/src/MigrationCreationTrait.php
+++ b/core/modules/migrate_drupal/src/MigrationCreationTrait.php
@@ -66,17 +66,20 @@ protected function getSystemData(array $database) {
   /**
    * Sets up the relevant migrations for import from a database connection.
    *
-   * @param array|\Drupal\Core\Database\Database $database
+   * @param array $database
    *   Database array representing the source Drupal database.
    * @param string $source_base_path
-   *   Address of the source Drupal site (e.g., http://example.com/).
+   *   (Optional) Address of the source Drupal site (e.g., http://example.com/).
    *
-   * @return int[]
-   *   An array of Migration entity IDs.
+   * @return array
+   *   An array of the migration templates (parsed YAML config arrays) that were
+   *   tagged for the identified source Drupal version. The templates are
+   *   populated with database state key and file source base path information
+   *   for execution. The array is keyed by migration IDs.
    *
    * @throws \Exception
    */
-  protected function getMigrationTemplates(array $database, $source_base_path) {
+  protected function getMigrationTemplates(array $database, $source_base_path = '') {
     // Set up the connection.
     $connection = $this->getConnection($database);
     if (!$drupal_version = $this->getLegacyDrupalVersion($connection)) {
@@ -112,7 +115,7 @@ protected function getMigrationTemplates(array $database, $source_base_path) {
    * migrations are returned.
    *
    * @param array $migration_templates
-   *   Migration template.
+   *   Migration templates (parsed YAML config arrays), keyed by the ID.
    *
    * @return \Drupal\migrate\Entity\MigrationInterface[]
    *   The migrations for import.
diff --git a/core/modules/migrate_drupal_ui/migrate_drupal_ui.install b/core/modules/migrate_drupal_ui/migrate_drupal_ui.install
index 6594ba6..8fb0783 100644
--- a/core/modules/migrate_drupal_ui/migrate_drupal_ui.install
+++ b/core/modules/migrate_drupal_ui/migrate_drupal_ui.install
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Install, update and uninstall functions for the migrate_drupal_ui module.
+ * Install, update, and uninstall functions for the migrate_drupal_ui module.
  */
 
 use Drupal\Core\Url;
diff --git a/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
index 7fa98ba..36e1e50 100644
--- a/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
@@ -708,8 +708,8 @@ public function buildOverviewForm(array $form, FormStateInterface $form_state) {
     if ($date_performed = $this->state->get('migrate_drupal_ui.performed')) {
       $form['upgrade_option_item'] = [
         '#type' => 'item',
-        '#prefix' => $this->t('<p>An upgrade has already been performed on this site.</p>'),
-        '#description' => $this->t('<p>Last upgrade: @date</p>', ['@date' => $this->dateFormatter->format($date_performed)]),
+        '#prefix' => '<p>' . $this->t('An upgrade has already been performed on this site.') . '</p>',
+        '#description' => '<p>' . $this->t('Last upgrade: @date', ['@date' => $this->dateFormatter->format($date_performed)]) . '</p>',
       ];
       $form['upgrade_option'] = array(
         '#type' => 'radios',
@@ -901,7 +901,7 @@ public function validateCredentialForm(array &$form, FormStateInterface $form_st
     }
 
     // Retrieve the database driver from the form, use reflection to get the
-    // namespace and then construct a valid database array the same as in
+    // namespace, and then construct a valid database array the same as in
     // settings.php.
     if ($driver = $form_state->getValue('driver')) {
       $drivers = $this->getDatabaseTypes();
@@ -923,7 +923,10 @@ public function validateCredentialForm(array &$form, FormStateInterface $form_st
     }
     else {
       $database = [];
-      // Find a migration which has database credentials and use those.
+      // Migration templates that had matching tags for the source Drupal
+      // version where converted to migration entities. Find one of those
+      // migrations to be able to look up the matching database credentials
+      // from state.
       $query = $this->entityStorage->getQuery('OR');
       $ids = $query->execute();
       foreach ($ids as $id) {
@@ -1019,7 +1022,7 @@ public function buildConfirmForm(array $form, FormStateInterface $form_state) {
     if ($rollback = $form_state->getValue('upgrade_option') == static::MIGRATE_UPGRADE_ROLLBACK) {
       $form_state->setStorage(['upgrade_option' => static::MIGRATE_UPGRADE_ROLLBACK]);
       $form['rollback'] = [
-        '#markup' => $this->t('All previously-imported content, as well as configuration such as field definitions, will be removed.'),
+        '#markup' => $this->t('All previously imported content, as well as configuration such as field definitions, will be removed.'),
       ];
       $form['actions']['submit']['#value'] = $this->t('Perform rollback');
     }
@@ -1039,6 +1042,8 @@ public function buildConfirmForm(array $form, FormStateInterface $form_state) {
         $destination_module = $this->moduleUpgradePaths[$template_id]['destination_module'];
         $table_data[$source_module][$destination_module][$migration_id] = $migration['label'];
       }
+      // Sort the table by source module names and within that destination
+      // module names.
       ksort($table_data);
       foreach ($table_data as $source_module => $destination_module_info) {
         ksort($table_data[$source_module]);
@@ -1049,7 +1054,7 @@ public function buildConfirmForm(array $form, FormStateInterface $form_state) {
       $form['missing_module_list_title'] = [
         '#type' => 'item',
         '#title' => $this->t('Missing upgrade paths'),
-        '#description' => $this->t('The following items will not be upgraded. For more information see <a href="https://www.drupal.org/upgrade/migrate"> Upgrading from Drupal 6 or 7 to Drupal 8</a>.'),
+        '#description' => $this->t('The following items will not be upgraded. For more information see <a href=":migrate">Upgrading from Drupal 6 or 7 to Drupal 8</a>.', array(':migrate' => 'https://www.drupal.org/upgrade/migrate')),
       ];
       $form['missing_module_list'] = [
         '#type' => 'table',
@@ -1214,7 +1219,7 @@ public function getCancelUrl() {
    * {@inheritdoc}
    */
   public function getDescription() {
-    return $this->t('<p><strong>Upgrade analysis report</strong></p>');
+    return '<p><strong>' . $this->t('Upgrade analysis report') . '</strong></p>';
   }
 
   /**
diff --git a/core/modules/migrate_drupal_ui/src/MigrateUpgradeRunBatch.php b/core/modules/migrate_drupal_ui/src/MigrateUpgradeRunBatch.php
index 69c0bf6..669ec5e 100644
--- a/core/modules/migrate_drupal_ui/src/MigrateUpgradeRunBatch.php
+++ b/core/modules/migrate_drupal_ui/src/MigrateUpgradeRunBatch.php
@@ -46,6 +46,8 @@ class MigrateUpgradeRunBatch {
   /**
    * The maximum length in seconds to allow processing in a request.
    *
+   * @see self::run()
+   *
    * @var int
    */
   protected static $maxExecTime;
@@ -264,7 +266,7 @@ protected static function displayResults($results) {
     $successes = $results['successes'];
     $failures = $results['failures'];
 
-    // If we had any successes lot that for the user.
+    // If we had any successes log that for the user.
     if ($successes > 0) {
       if ($results['operation'] == 'import') {
         drupal_set_message(static::getTranslation()->formatPlural($successes, 'Completed 1 upgrade task successfully', 'Completed @count upgrade tasks successfully'));
diff --git a/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
index ca8d213..a4911aa 100644
--- a/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
+++ b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
@@ -43,7 +43,7 @@ protected function setUp() {
     $this->sourceDatabase = Database::getConnection('default', 'migrate_drupal_ui');
 
     // Create and log in as user 1. Migrations in the UI can only be performed
-    // as user 1.
+    // as user 1 once https://www.drupal.org/node/2675066 lands.
     $this->drupalLogin($this->rootUser);
   }