edlp_d8/core/lib/Drupal/Core/Render/Element/Fieldgroup.php

<?php

namespace Drupal\Core\Render\Element;

/**
 * Provides a render element for a group of form elements.
 *
 * In default rendering, the only difference between a 'fieldgroup' and a
 * 'fieldset' is the CSS class applied to the containing HTML element. Normally
 * use a fieldset.
 *
 * @see \Drupal\Core\Render\Element\Fieldset for documentation and usage.
 *
 * @see \Drupal\Core\Render\Element\Fieldset
 * @see \Drupal\Core\Render\Element\Details
 *
 * @RenderElement("fieldgroup")
 */
class Fieldgroup extends Fieldset {

  public function getInfo() {
    return [
      '#attributes' => ['class' => ['fieldgroup']],
    ] + parent::getInfo();
  }

}