{%- comment -%}
  The trail above a manual page's title: the manual's root, then the page's
  section, then, for a page under a chapter (`parent:`), that chapter. A
  chapter's own title is right underneath, so it is not repeated
  as a crumb. The last crumb is where you are and does not link.

  Replaces the theme's breadcrumbs, which read `parent:` front matter the
  chapters do not have; sections come from site.manual.sections and the
  page a section has is the one _plugins/manual.rb makes for it.
{%- endcomment -%}
{%- if page.url contains "/manual/" -%}
{%- assign crumb_key = page.section | default: page.section_key -%}
{%- assign crumb_section = nil -%}
{%- for section in site.manual.sections -%}
  {%- if section.key == crumb_key -%}{%- assign crumb_section = section -%}{%- endif -%}
{%- endfor -%}
{%- assign section_page = site.html_pages | where: "section_key", crumb_key | first -%}
<nav class="crumbs" aria-label="Breadcrumb">
  <ol class="crumbs-list">
    <li class="crumbs-item">
      {%- if page.url == "/manual/" -%}
      <span aria-current="page">Manual</span>
      {%- else -%}
      <a href="{{ '/manual/' | relative_url }}">Manual</a>
      {%- endif -%}
    </li>
    {%- if crumb_section %}
    <li class="crumbs-item">
      {%- if page.section_key or section_page == nil -%}
      <span aria-current="page">{{ crumb_section.label }}</span>
      {%- else -%}
      <a href="{{ section_page.url | relative_url }}">{{ crumb_section.label }}</a>
      {%- endif -%}
    </li>
    {%- endif %}
    {%- if page.parent %}
    {%- assign parent_url = "/manual/" | append: page.parent | append: "/" %}
    {%- assign parent_page = site.html_pages | where: "url", parent_url | first %}
    {%- if parent_page %}
    <li class="crumbs-item">
      <a href="{{ parent_page.url | relative_url }}">{{ parent_page.title }}</a>
    </li>
    {%- endif %}
    {%- endif %}
  </ol>
</nav>
{%- endif -%}