* to TRUE.
* @param bool|null $keep_untranslatable_fields
* (optional) Whether untranslatable field values should be kept or copied
- * from the default revision when generating a merged revision.
+ * from the default revision when generating a merged revision. Defaults to
+ * TRUE if the provided entity is the default translation and untranslatable
+ * fields should only affect the default translation, FALSE otherwise.
*
* @return \Drupal\Core\Entity\EntityInterface|\Drupal\Core\Entity\RevisionableInterface
* A new translatable entity revision object.