diff --git a/core/modules/field_ui/field_ui.api.php b/core/modules/field_ui/field_ui.api.php
index ef9e338..5277bce 100644
--- a/core/modules/field_ui/field_ui.api.php
+++ b/core/modules/field_ui/field_ui.api.php
@@ -185,6 +185,15 @@ function hook_field_formatter_settings_form($field, $instance, $view_mode, $form
  *   - 'form': The (entire) configuration form array.
  */
 function hook_field_formatter_settings_form_alter(&$element, &$form_state, $context) {
+  // Add a mysetting checkbox to the settings form for foo_field fields.
+  if ($context['field']['type'] == 'foo_field') {
+    $display = $context['instance']['display'][$context['view_mode']];
+    $element['mysetting'] = array(
+      '#type' = 'checkbox',
+      '#title' = t('My setting'),
+      '#default_value' = $display['settings']['mysetting'],
+    );
+  }
 }
 
 /**
@@ -199,6 +208,14 @@ function hook_field_formatter_settings_form_alter(&$element, &$form_state, $cont
  *   - 'view_mode': The view mode being configured.
  */
 function hook_field_formatter_settings_summary_alter(&$summary, $context) {
+  // Append a message to the summary when an instance of foo_field has
+  // mysetting set to TRUE for the current view mode.
+  if ($context['field']['type'] == 'foo_field') {
+    $display = $context['instance']['display'][$context['view_mode']];
+    if ($display['settings']['mysetting']) {
+      $summary .= '<br />' . t('My setting enabled.');
+    }
+  }
 }
 
 /**
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
index 1bf2a99..e15f079 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageDisplayTest.php
@@ -76,19 +76,21 @@ class ManageDisplayTest extends FieldUiTestBase {
     $this->assertEqual($current_format, $format, t('The formatter was updated.'));
     $this->assertEqual($current_setting_value, $setting_value, t('The setting was updated.'));
 
-    // Assert hook_field_formatter_settings_summary_alter is called.
+    // Assert that hook_field_formatter_settings_summary_alter() is called.
     $this->assertText('field_test_field_formatter_settings_summary_alter');
 
-    // Click on the formatter settings button to open the formatter settings form.
+    // Click on the formatter settings button to open the formatter settings
+    // form.
     $this->drupalPostAJAX(NULL, array(), "field_test_formatter_settings_edit");
 
-    // Assert the field added in field_test_field_formatter_settings_form_alter is present.
+    // Assert that the field added in
+    // field_test_field_formatter_settings_form_alter() is present.
     $fieldname = 'fields[field_test][settings_edit_form][settings][field_test_formatter_settings_form_alter]';
-    $this->assertField($fieldname, t('Field added in hook_ield_formatter_settings_form_alter is present.'));
+    $this->assertField($fieldname, 'The field added in hook_field_formatter_settings_form_alter() is present on the settings form.'));
     $edit = array($fieldname => 'foo');
     $this->drupalPostAJAX(NULL, $edit, "field_test_formatter_settings_update");
 
-    // Open the formatter settings form again to check if the settings are updated.
+    // Confirm that the settings are updated on the settings form.
     $this->drupalPostAJAX(NULL, array(), "field_test_formatter_settings_edit");
     $this->assertFieldByName($fieldname, 'foo');
   }