--- /dev/null
+<?php
+
+namespace Drupal\settings_tray_test\Form;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormBase;
+
+/**
+ * @see \Drupal\settings_tray_test\Plugin\Block\SettingsTrayFormAnnotationIsClassBlock
+ */
+class SettingsTrayFormAnnotationIsClassBlockForm extends PluginFormBase {
+
+ /**
+ * The block plugin.
+ *
+ * @var \Drupal\Core\Block\BlockPluginInterface
+ */
+ protected $plugin;
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+ $form = $this->plugin->buildConfigurationForm($form, $form_state);
+
+ $form['some_setting'] = [
+ '#type' => 'select',
+ '#title' => t('Some setting'),
+ '#options' => [
+ 'a' => 'A',
+ 'b' => 'B',
+ ],
+ '#required' => TRUE,
+ ];
+
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {}
+
+}