canBuildGroup example

  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($form, $form_state);
    if ($this->canExpose()) {
      $this->showExposeButton($form, $form_state);
    }
    if ($this->canBuildGroup()) {
      $this->showBuildGroupButton($form, $form_state);
    }
    $form['clear_markup_start'] = [
      '#markup' => '<div class="clearfix">',
    ];
    if ($this->isAGroup()) {
      if ($this->canBuildGroup()) {
        $form['clear_markup_start'] = [
          '#markup' => '<div class="clearfix">',
        ];
        // Render the build group form.