Builds a simple form to test the #group property on #type 'vertical_tabs'.
function form_test_group_vertical_tabs() {
$form['vertical_tabs'] = array(
'#type' => 'vertical_tabs',
);
$form['meta'] = array(
'#type' => 'details',
'#title' => 'First group element',
'#group' => 'vertical_tabs',
);
$form['meta']['element'] = array(
'#type' => 'textfield',
'#title' => 'First nested element in details element',
);
$form['meta_2'] = array(
'#type' => 'details',
'#title' => 'Second group element',
'#group' => 'vertical_tabs',
);
$form['meta_2']['element_2'] = array(
'#type' => 'textfield',
'#title' => 'Second nested element in details element',
);
return $form;
}