{#- The shell PARTIAL (lifeboat.md §18): three parameters — viewer line, nav, scheme switch — each
    may be absent, and an absent one renders nothing. -#}
<header>
  <p class="shell">{{ shell.container_line }}</p>
  {%- if shell.viewer_line %}
  <p class="viewer">{{ shell.viewer_line }}</p>
  {%- endif %}
  {%- if shell.window %}
  <p class="window{% if shell.window.state == 'lapsed' %} alarm-text{% endif %}" role="status">{{ shell.window.text }}</p>
  {%- endif %}
  {%- if shell.nav %}
  <nav aria-label="egzos">
    {%- for n in shell.nav %}
    <a href="{{ n.href }}"{% if n.current %} aria-current="page"{% endif %}>{{ n.label }}</a>
    {%- endfor %}
  </nav>
  {%- endif %}
  {%- if shell.scheme %}
  <form class="scheme" method="post" action="/prefs">
    <input type="hidden" name="csrf" value="{{ shell.scheme.csrf }}">
    <input type="hidden" name="return" value="{{ shell.scheme.return }}">
    {%- for value, key in [("light", "scheme.light"), ("dark-neutral", "scheme.darkNeutral"), ("dark-violet", "scheme.darkViolet")] %}
    <button name="scheme" value="{{ value }}" aria-pressed="{{ 'true' if shell.scheme.current == value else 'false' }}">{{ S[key] }}</button>
    {%- endfor %}
  </form>
  {%- endif %}
</header>