diff --git a/core/modules/editor/js/editor.dialog.js b/core/modules/editor/js/editor.dialog.js
index ad44c4b..b52add1 100644
--- a/core/modules/editor/js/editor.dialog.js
+++ b/core/modules/editor/js/editor.dialog.js
@@ -31,8 +31,14 @@
     $(window).trigger('editor:dialogsave', [response.values]);
   };
 
+  /**
+   * Add change event to source radio buttons.
+   *
+   * It toggles display of url and file field depending on selected source.
+   */
   Drupal.behaviors.imageSourceChange = {
     attach: function (context, settings) {
+      // Change event on the source radio buttons.
       $('input[name=source]', context).change(function () {
         $('#fid-field', context).toggleClass('hidden');
         $('#src-field', context).toggleClass('hidden');
diff --git a/core/modules/editor/src/Form/EditorImageDialog.php b/core/modules/editor/src/Form/EditorImageDialog.php
index d511e86..7889eef 100644
--- a/core/modules/editor/src/Form/EditorImageDialog.php
+++ b/core/modules/editor/src/Form/EditorImageDialog.php
@@ -96,6 +96,8 @@ public function buildForm(array $form, FormStateInterface $form_state, FilterFor
     $existing_file = isset($image_element['data-entity-uuid']) ? \Drupal::entityManager()->loadEntityByUuid('file', $image_element['data-entity-uuid']) : NULL;
     $fid = $existing_file ? $existing_file->id() : NULL;
 
+    // Radio buttons to select the image source: url or file. This is only
+    // displayed if the editor has image uploads enabled.
     $form['source'] = array(
       '#title' => $this->t('Source'),
       '#type' => 'radios',
@@ -138,8 +140,7 @@ public function buildForm(array $form, FormStateInterface $form_state, FilterFor
       '#suffix' => '</div>',
     );
 
-    // If the editor has image uploads enabled, show a managed_file form item,
-    // otherwise show a (file URL) text form item.
+    // If the editor has image uploads enabled, show a managed_file form item.
     if (!$image_upload['status']) {
       $form['fid']['#access'] = FALSE;
       $form['fid']['#required'] = FALSE;