Document strip_anchors plugin in pelican theme post

Added new section explaining the homepage summary filtering plugin
that strips TOC anchor links from article summaries. Includes:

- Why the problem exists (RST generates anchor links in TOC)
- How the plugin solves it (strip_anchors Jinja2 filter)
- Implementation details with code examples
- Template usage example

This plugin prevents broken anchor links in homepage excerpts.

content/2025-10-11-pelican-theme-upgrade-right-sidebar-toc.rst

@@ -86,6 +86,63 @@ When the TOC is present, the main content width adjusts using the ``:has()`` pse
    width: 65%;
  }
 
+homepage summary filtering
+===========================
+
+ReStructuredText automatically generates anchor links in section headings when a table of contents is present. These anchors work perfectly on article pages, but become broken links when article summaries appear on the homepage - the anchor targets don't exist in that context.
+
+To solve this, I created a Pelican plugin that provides a ``strip_anchors`` Jinja2 filter. This filter removes TOC divs and ``toc-backref`` anchor links from article summaries before they're rendered on the homepage.
+
+**The Plugin**
+
+The plugin (``lib/strip_toc_summary.py``) uses regex to strip problematic HTML:
+
+.. code-block:: python
+
+ def strip_anchors(text):
+     """Jinja2 filter to strip TOC and anchor links from HTML text."""
+     if not text:
+         return text
+
+     # Remove the entire <div class="contents"> ... </div> block
+     text = re.sub(
+         r'<div\s+class="contents[^"]*"[^>]*>.*?</div>',
+         '',
+         text,
+         flags=re.DOTALL | re.IGNORECASE
+     )
+
+     # Remove anchor links from headings
+     # Converts <a class="toc-backref" href="#id1">text</a> to just text
+     text = re.sub(
+         r'<a[^>]*class="[^"]*toc-backref[^"]*"[^>]*>(.*?)</a>',
+         r'\1',
+         text,
+         flags=re.DOTALL | re.IGNORECASE
+     )
+
+     return text
+
+**Template Usage**
+
+The filter is applied in the theme's ``index.html`` template:
+
+.. code-block:: jinja
+
+ <div class="article_text">
+   {{ article.summary | strip_anchors }}
+ </div>
+
+This approach ensures that:
+
+1. Article pages retain their TOC anchor links for proper navigation
+2. Homepage summaries display clean headings without broken links
+3. The filtering happens at template render time, not during content generation
+
+**Why This Matters**
+
+Without this filter, homepage excerpts would contain links like ``<a href="#the-design">the design</a>`` that point to anchors that don't exist on the homepage. This creates a poor user experience with broken navigation. The filter strips these anchors while preserving the heading text, resulting in clean, functional homepage previews.
+
 dark mode implementation
 ========================