Build the options form.
Overrides String::buildOptionsForm
public function buildOptionsForm(&$form, &$form_state) {
parent::buildOptionsForm($form, $form_state);
$form['summary']['human'] = array(
'#title' => t('Display list value as human readable'),
'#type' => 'checkbox',
'#default_value' => $this->options['summary']['human'],
'#states' => array(
'visible' => array(
':input[name="options[default_action]"]' => array(
'value' => 'summary',
),
),
),
);
}