'#multiple' => TRUE,
];
+ $form['opt_groups'] = [
+ '#type' => 'select',
+ '#options' => [
+ 'optgroup_one' => ['one' => 'one', 'two' => 'two', 'three' => 'three', 'four' => '<strong>four</strong>'],
+ 'optgroup_two' => ['five' => 'five', 'six' => 'six'],
+ ],
+ ];
+
$form['submit'] = ['#type' => 'submit', '#value' => 'Submit'];
return $form;
}