diff -u b/core/includes/form.inc b/core/includes/form.inc --- b/core/includes/form.inc +++ b/core/includes/form.inc @@ -303,6 +303,7 @@ function template_preprocess_fieldset(&$variables) { $element = $variables['element']; Element::setAttributes($element, array('id')); + Element\RenderElement::setAttributes($element); $variables['attributes'] = $element['#attributes']; $variables['prefix'] = isset($element['#field_prefix']) ? $element['#field_prefix'] : NULL; $variables['suffix'] = isset($element['#field_suffix']) ? $element['#field_suffix'] : NULL; diff -u b/core/modules/system/templates/fieldset.html.twig b/core/modules/system/templates/fieldset.html.twig --- b/core/modules/system/templates/fieldset.html.twig +++ b/core/modules/system/templates/fieldset.html.twig @@ -5,8 +5,7 @@ * * Available variables: * - attributes: HTML attributes for the fieldset element. - * - required: The required marker or empty if the associated fieldset is - * not required. + * - required: Boolean indicating whether the fieldeset element is required. * - legend: The legend element containing the following properties: * - title: Title of the fieldset, intended for use as the text of the legend. * - attributes: HTML attributes to apply to the legend.