{#  https://api.drupal.org/api/drupal/core!modules!system!templates!menu.html.twig/8
    menu_name: The machine name of the menu.
    items: A nested list of menu items. Each menu item contains:
      attributes: HTML attributes for the menu item.
      below: The menu item child items.
      title: The menu link title.
      url: The menu link url, instance of \Drupal\Core\Url
      localized_options: Menu link localized options.
#}

{# All menu and submenu items #}
<div class="navbar">
  <div class="navbar-header pull-right">
    <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
      <span class="icon-bar"></span>
      <span class="icon-bar"></span>
      <span class="icon-bar"></span>
    </button>
    <div class="collapse navbar-collapse">
      {% import _self as menus %}
      {#
        We call a macro which calls itself to render the full tree.
        @see http://twig.sensiolabs.org/doc/tags/macro.html
      #}
      {{ menus.menu_links(items, attributes, 0) }}

      {% macro menu_links(items, attributes, menu_level) %}
        {% import _self as menus %}
        {% if items %}
          {% if menu_level == 0 %}
            <ul class="nav navbar-nav" role="menu" aria-labelledby="dropdownMenu">
          {% else %}
            <ul class="dropdown-menu" role="menu" aria-labelledby="dLabel">
          {% endif %}
          {% for item in items %}
            {% if item.below %}
              {% if menu_level == 0 %}
                <li class="dropdown">
                  <a href="{{ item.url }}" class="dropdown-toggle">{{ item.title }} <span class="caret"></span></a>
                  {{ menus.menu_links(item.below, attributes, menu_level + 1) }}
                </li>
              {% else %}
                <li class="dropdown-submenu">
                  <a href="{{ item.url }}">{{ item.title }}</a>
                  {{ menus.menu_links(item.below, attributes, menu_level + 1) }}
                </li>
              {% endif %}
            {% else %}
              <li {{ item.attributes }}>{{ link(item.title, item.url) }}</li>
            {% endif %}
          {% endfor %}
          </ul>
        {% endif %}
      {% endmacro %}

    </div>
  </div>
</div>