dsfr4drupal-1.x-dev/components/tab-panel/tab-panel.twig

{% set attributes = attributes.setAttribute('tabindex', "-1") %}
{% set selected = selected ?? false %}

{% if selected %}
  {% set attributes = attributes.setAttribute('tabindex', "0").addClass('fr-tabs__panel--selected') %}
{% endif %}

<div{{ attributes.addClass('fr-tabs__panel').setAttribute('role', 'tabpanel').setAttribute('id', html_id).setAttribute('aria-labelledby', tab_id) }}>
  {{ content }}
</div>