public function buildOptionsForm(&$form, FormStateInterface $form_state)
 {
     parent::buildOptionsForm($form, $form_state);
     $form['info'] = array('#markup' => '<p class="description">Attempt to pull bounding box info
   directly from the query string, bypassing Drupal\'s normal argument
   handling. If the argument does not exist, all values will be shown.</p>');
     $form['arg_id'] = array('#type' => 'textfield', '#title' => t('Query argument ID'), '#size' => 60, '#maxlength' => 64, '#default_value' => $this->options['arg_id'] ? $this->options['arg_id'] : t('bbox'), '#description' => t('The ID of the query argument.<br />For OpenLayers use <em>bbox</em>, (as in "<em>?bbox=left,bottom,right,top</em>".)'));
 }