Issue #3370179 by fago, Wim Leers, borisson_, smustgrave: Clarify why...

Issue #3370179 by fago, Wim Leers, borisson_, smustgrave: Clarify why FieldConfigBase::getDataType() is 'list' and not 'field_config_base'

core/lib/Drupal/Core/Field/FieldConfigBase.php

@@ -490,6 +490,12 @@ public static function createFromDataType($type) {
    * {@inheritdoc}
    */
   public function getDataType() {
+    // This object serves as data definition for field item lists, thus
+    // the correct data type is 'list'. This is not to be confused with
+    // the config schema type, 'field_config_base', which is used to
+    // describe the schema of the configuration backing this objects.
+    // @see \Drupal\Core\Field\FieldItemList
+    // @see \Drupal\Core\TypedData\DataDefinitionInterface
     return 'list';
   }