diff --git a/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
index cab863b..e8ff98e 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
@@ -317,8 +317,8 @@ public function save() {
       $this->module = $field_type['module'];
       $this->active = 1;
 
-      // Create all per-field-type properties (needed here as long as we have
-      // settings that impact column definitions).
+      // Make sure all settings are present, so that a complete field
+      // definition is passed to the various hooks and written to config.
       $this->settings += $field_type['settings'];
 
       // Provide default storage.
@@ -369,8 +369,9 @@ public function save() {
       $module_handler->invokeAll('field_update_forbid', array($this, $original, $has_data));
 
       // Tell the storage engine to update the field by invoking the
-      // hook_field_storage_update_field(). Do this before saving the
-      // new definition since it still might fail.
+      // hook_field_storage_update_field(). The storage engine can reject the
+      // definition update as invalid by raising an exception, which stops
+      // execution before the definition is written to config.
       $module_handler->invoke($this->storage['module'], 'field_storage_update_field', array($this, $original, $has_data));
 
       $hook = 'field_update_field';