just-the-docs/_includes/components/breadcrumbs.html

{%- comment -%}
  Include as: {%- include components/breadcrumbs.html -%}
  Depends on: page, site.
  Includes: components/site_nav.html.
  Results in: HTML for the breadcrumbs component.
  Overwrites:
    nav_list_link, site_nav, nav_list_simple, nav_list_link_class, nav_category,
    nav_anchor_splits, nav_breadcrumbs, nav_split, nav_split_next, nav_split_test,
    nav_breadcrumb_link, nav_list_end_less, nav_list_end_count, nav_end_index, nav_breadcrumb.
{%- endcomment -%}

{%- if page.url != "/" and page.parent and page.title -%}

{%- capture site_nav -%}
{%- include_cached components/site_nav.html all=true -%}
{%- endcapture -%}

{%- capture nav_list_link -%}
<a href="{{ page.url | relative_url }}" class="nav-list-link">
{%- endcapture -%}

{%- capture nav_list_simple -%}
<ul class="nav-list">
{%- endcapture -%}

{%- capture nav_list_link_class %} class="nav-list-link">
{%- endcapture -%}

{%- capture nav_category -%}
<div class="nav-category">
{%- endcapture -%}

{%- assign nav_anchor_splits =
      site_nav | split: nav_list_link |
      first | split: nav_category |
      last | split: "</a>" -%}

{%- comment -%}
  The ordinary pages (if any) and the collections pages (if any) are separated by
  occurrences of nav_category.
  
  Any ancestor nav-links of the page are contained in the last group of pages,
  immediately preceding nav-lists. After splitting at "</a>", the anchor that
  was split is a potential ancestor link when the following split starts with
  a nav-list. 
  
  The array nav_breadcrumbs is the stack of current potential ancestors of the
  current page. A split that contains one or more "</ul>"s requires that number
  of potential ancestors to be popped from the stack.
  
  The number of occurrences of a string in nav_split_next is computed by removing
  them all, then dividing the resulting size difference by the length of the string.
{%- endcomment %}

{%- assign nav_breadcrumbs = "" | split: "" -%}

{%- for nav_split in nav_anchor_splits -%}
{%- unless forloop.last -%}

{%- assign nav_split_next = nav_anchor_splits[forloop.index] | strip -%}

{%- assign nav_split_test =
      nav_split_next | remove_first: nav_list_simple | prepend: nav_list_simple -%}
{%- if nav_split_test == nav_split_next -%}
  {%- assign nav_breadcrumb_link =
        nav_split | split: "<a " | last | prepend: "<a " |
        replace: nav_list_link_class, ">" | append: "</a>" -%}
  {%- assign nav_breadcrumbs = nav_breadcrumbs | push: nav_breadcrumb_link -%}
{%- endif -%}

{%- if nav_split_next contains "</ul>" -%}
  {%- assign nav_list_end_less = nav_split_next | remove: "</ul>" -%}
  {%- assign nav_list_end_count =
        nav_split_next.size | minus: nav_list_end_less.size | divided_by: 5 -%}
  {% for nav_end_index in (1..nav_list_end_count) %}
    {%- assign nav_breadcrumbs = nav_breadcrumbs | pop -%}
  {%- endfor -%}
{%- endif -%}

{%- endunless -%}
{%- endfor -%}

<nav aria-label="Breadcrumb" class="breadcrumb-nav">
  <ol class="breadcrumb-nav-list">
    {%- for nav_breadcrumb in nav_breadcrumbs %}
    <li class="breadcrumb-nav-list-item">{{ nav_breadcrumb }}</li>
    {%- endfor %}
    <li class="breadcrumb-nav-list-item"><span>{{ page.title }}</span></li>
  </ol>
</nav>

{% if site.nav_error_report %}
{{ nav_error_report }}
{% endif %}

{%- endif -%}