diff --git a/core/modules/translation_entity/lib/Drupal/translation_entity/Form/TranslatableForm.php b/core/modules/translation_entity/lib/Drupal/translation_entity/Form/TranslatableForm.php
index 82eddbe..3eca1c5 100644
--- a/core/modules/translation_entity/lib/Drupal/translation_entity/Form/TranslatableForm.php
+++ b/core/modules/translation_entity/lib/Drupal/translation_entity/Form/TranslatableForm.php
@@ -79,7 +79,22 @@ public function buildForm(array $form, array &$form_state, $field_name = NULL) {
   }
 
   /**
-   * {@inheritdoc}
+   * Form submission handler.
+   *
+   * This submit handler maintains consistency between the translatability of an
+   * entity and the language under which the field data is stored. When a field
+   * is marked as translatable, all the data in
+   * $entity->{field_name}[Language::LANGCODE_NOT_SPECIFIED] is moved to
+   * $entity->{field_name}[$entity_language]. When a field is marked as
+   * untranslatable the opposite process occurs. Note that marking a field as
+   * untranslatable will cause all of its translations to be permanently
+   * removed, with the exception of the one corresponding to the entity
+   * language.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param array $form_state
+   *   An associative array containing the current state of the form.
    */
   public function submitForm(array &$form, array &$form_state) {
     // This is the current state that we want to reverse.