diff -u b/core/modules/text/src/Plugin/Field/FieldType/TextFieldItemList.php b/core/modules/text/src/Plugin/Field/FieldType/TextFieldItemList.php
--- b/core/modules/text/src/Plugin/Field/FieldType/TextFieldItemList.php
+++ b/core/modules/text/src/Plugin/Field/FieldType/TextFieldItemList.php
@@ -6,7 +6,7 @@
 use Drupal\Core\Form\FormStateInterface;
 
 /**
- * Represents a configurable entity text field.
+ * Defines an item list class for text fields.
  */
 class TextFieldItemList extends FieldItemList {
 
@@ -17,12 +17,15 @@
     if ($allowed_formats = $this->getSetting('allowed_formats')) {
       if (!empty($allowed_formats)) {
         $field_name = $this->definition->getName();
-        $submitted_values = $form_state->getValue(['default_value_input', $field_name]);
+        $submitted_values = $form_state->getValue([
+          'default_value_input',
+          $field_name,
+        ]);
         foreach ($submitted_values as $delta => $value) {
           if (!in_array($value['format'], $allowed_formats)) {
             $form_state->setErrorByName(
               "default_value_input][{$field_name}][{$delta}][format",
-              t("The selected text format is not allowed.")
+               $this->t("The selected text format is not allowed.")
             );
           }
         }
diff -u b/core/modules/text/src/Plugin/Field/FieldType/TextItemBase.php b/core/modules/text/src/Plugin/Field/FieldType/TextItemBase.php
--- b/core/modules/text/src/Plugin/Field/FieldType/TextItemBase.php
+++ b/core/modules/text/src/Plugin/Field/FieldType/TextItemBase.php
@@ -6,8 +6,8 @@
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemBase;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
-use Drupal\Core\TypedData\DataDefinition;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\TypedData\DataDefinition;
 
 /**
  * Base class for 'text' configurable field types.
@@ -43,10 +43,9 @@
   /**
    * Render API callback: Processes the allowed formats value.
    *
-   * Ensure the element's value is an indexed array of selected format IDs.
+   * Ensure the element's value is an indexed array of selected format IDs. This function is assigned as an #element_validate callback.
    *
-   * This function is assigned as an #element_validate callback in
-   * ::fieldSettingsForm().
+   * @see static::fieldSettingsForm()
    */
   public static function validateAllowedFormats(array &$element, FormStateInterface $form_state) {
     $value = array_values(array_filter($element['#value']));