Default options form that provides the label widget that all fields should have.
Overrides HandlerBase::buildOptionsForm
public function buildOptionsForm(&$form, &$form_state) {
parent::buildOptionsForm($form, $form_state);
$form['label'] = array(
'#type' => 'textfield',
'#title' => t('Identifier'),
'#default_value' => isset($this->options['label']) ? $this->options['label'] : '',
'#description' => t('Edit the administrative label displayed when referencing this relationship from filters, etc.'),
'#required' => TRUE,
);
$form['required'] = array(
'#type' => 'checkbox',
'#title' => t('Require this relationship'),
'#description' => t('Enable to hide items that do not contain this relationship'),
'#default_value' => !empty($this->options['required']),
);
}