docs: keep nested toc

for a better overview. Auto-expansion on scrolling is still left as a todo.

docs/theme/partials/toc-item.html

@@ -1,16 +1,56 @@
+<!--
+     Copyright (c) 2016-2024 Martin Donath <martin.donath@squidfunk.com>
+
+     Permission is hereby granted, free of charge, to any person obtaining a copy
+     of this software and associated documentation files (the "Software"), to
+     deal in the Software without restriction, including without limitation the
+     rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+     sell copies of the Software, and to permit persons to whom the Software is
+     furnished to do so, subject to the following conditions:
+
+     The above copyright notice and this permission notice shall be included in
+     all copies or substantial portions of the Software.
+
+     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+     IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+     FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+     AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+     LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+     FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+     IN THE SOFTWARE.
+-->
+
+<!-- Table of contents item -->
 <li class="md-nav__item">
-    <a href="{{ toc_item.url }}" class="md-nav__link">
-      <span class="md-ellipsis">
-        {{ toc_item.title | replace(".", ".<wbr>")}}
-      </span>
-    </a>
-    {% if toc_item.children %}
-      <nav class="md-nav" aria-label="{{ toc_item.title | striptags }}">
-        <ul class="md-nav__list">
-          {% for toc_item in toc_item.children %}
-            {% include "partials/toc-item.html" %}
-          {% endfor %}
-        </ul>
-      </nav>
-    {% endif %}
+    {%- set should_collapse = toc_item.level > 2 and toc_item.children -%}
+    {% if should_collapse -%}
+    <details>
+        <summary>
+            {%- endif %}
+            <a href="{{ toc_item.url }}" class="md-nav__link">
+                <span class="md-ellipsis">
+                    {%- if page.url.split("/")[-3] == "reference" -%}
+                    {{ toc_item.title.split(".")[-1] }}
+                    {%- else -%}
+                    {{ toc_item.title }}
+                    {%- endif -%}
+                </span>
+            </a>
+         {% if should_collapse -%}
+        </summary>
+        {%- endif %}
+
+        <!-- Table of contents list -->
+        {% if toc_item.children %}
+        <nav class="md-nav" aria-label="{{ toc_item.title | striptags }}">
+            <ul class="md-nav__list">
+                {% for toc_item in toc_item.children %}
+                {% include "partials/toc-item.html" %}
+                {% endfor %}
+            </ul>
+        </nav>
+        {% endif %}
+        {% if should_collapse -%}
+    </details>
+    {%- endif %}
 </li>