tabs.html

<div class="row docs-nav">
  <div class="col-sm-8">
    <ul class="nav nav-tabs visible-md-block visible-lg-block">
      {% assign release_version = page.path | split:"/" | slice:1 | first %}
      {% for tab in site.data.doc_categories[release_version] %}
          {% assign tab_title_with_version = tab.title | append:" (" | append:release_version | append:")" %}
          <li {% if page.category == tab_title_with_version %}class="active"{% endif %}>
          <a href="{{ site.baseurl }}/{{ tab.href | replace:'$$VERSION$$',release_version }}">
            {{ tab.title }}
          </a>
        </li>
      {% endfor %}
    </ul>
    <ol class="breadcrumb visible-xs-block visible-sm-block">
      <li><a href="{{ site.baseurl }}/docs/{{ release_version }}/">Docs</a></li>
      <li class="active">{{ page.category }}</li>
    </ol>
  </div>
  <div class="col-sm-4 version-dropdown">
    <div class="btn-group" id="version-dropdown" style="margin-top: 1px; margin-bottom: 0; margin-right: 30px">
      <a data-target="#version-dropdown" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-expanded="false">
        {{ release_version }}
        <span class="caret"></span>
      </a>
      <ul class="dropdown-menu">
        {% comment %}
          Liquid does not gives us an easy way to split a string at a specific
          occurrence of a character, and keep the rest. Therefore, we use the
          hack below.

          'doc_name' is the document's name with repesct to Jekyll: where it
          resides on the disk. The name looks something like:

            "_docs/v0.0/dir/name/file.md"

          The 'doc_name' is the portion of the file path after the top-level
          _docs/ and version directory. It's how we access the inverted index to
          tell which versions this document belongs to; it stays the same
          between versions.

          So, we split on slashes, and keep everything starting from the 2nd 
          index to the end. Hence the magic number '999' is meant to make sure
          even deep hierarchies are kept.

          We do the same with the 'url_name' for purposes of linking the specific
          version of this file, except the URL structure looks like:

            baseurl/docs/v0.0/dir/name/file/index.html

          possibly, and we do not want the trailing "index.html".
        {% endcomment %}
        {% assign doc_name = page.path | split:"/" | slice:2,999 | join:"/" %}
        {% assign url_name = page.url | split:"/" | slice:3,999 | join:"/" | remove:"index.html" %}
        
        {% assign versions = site.data.doc_version_index[doc_name] | unshift:'latest' %}
        {% unless versions %}
          {% assign versions = 'latest' | split:' ' %}
        {% endunless %}

        {% for version in versions %}
          <li {% if release_version == version %}class="active"{% endif %}><a href="{{ site.baseurl }}/docs/{{ version }}/{{ url_name }}">{{ version }}</a></li>
        {% endfor %}
      </ul>
    </div>
    <div class="edit-on-github visible-lg-inline-block visible-md-inline-block">
      {% assign filename = page.path | split:"/" | last | downcase %}
      <a class="icon github" href="{{ site.github.repository_url }}/edit/forsetisecurity.org/{{ page.path }}">
        Edit this page
      </a>
    </div>
  </div>
</div>