From 1b084ecb28a78dbdd8275fe1d8c7cf249485cf94 Mon Sep 17 00:00:00 2001
From: Daniel Fancsali <fancsali@gmail.com>
Date: Tue, 24 Mar 2020 22:30:27 +0000
Subject: [PATCH] Selective disable for one heading

---
 README.md                | 11 +++++++++++
 mdx_headdown/__init__.py | 16 ++++++++++++----
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 6f24ec6..988cc29 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,17 @@ MARKDOWN = {
 ...
 ```
 
+You can selectively disable processing of a particular heading by adding the `headdown="0"` attribute to it:
+
+```html
+<h1 headdown="1">This will remain level 1!</h1>
+```
+
+... or using the `attr_list` extension:
+```markdown
+# This one stays at level 1 { headdown='0'}
+```
+
 ## Credit
 
 Thanks are owed to the author of [mdx_downheader][p2], whose code I examined for inspiration; and the contributers to the [default python-markdown extensions][pmdx], whose code I examined to get a better idea of what the [manual][pmdapi] was talking about.
diff --git a/mdx_headdown/__init__.py b/mdx_headdown/__init__.py
index 2fdd94e..5c9b75f 100644
--- a/mdx_headdown/__init__.py
+++ b/mdx_headdown/__init__.py
@@ -11,6 +11,7 @@
 # Import relevant modules.
 from markdown.extensions import Extension
 from markdown.postprocessors import Postprocessor
+from xml.etree import ElementTree as ET
 import re
 
 name = "mdx_headdown"
@@ -22,13 +23,20 @@ def run(self, text):
         self.offset = abs(int(self.config['offset']))
 
         # Match headings 1-6 case insensitively, and capture the heading number.
-        heading_pattern = re.compile(r'<h([1-6])>([^<]*)</h\1>', re.I)
+        heading_pattern = re.compile(r'<h([1-6])[^>]*>([^<]*)</h\1>', re.I)
 
         return re.sub(heading_pattern, self.downgrade, text)
 
-    def downgrade(self, mo):
-        return '<h%(level)d>%(content)s</h%(level)d>' % \
-                {'level': min(6, int(mo.group(1)) + self.offset), 'content': mo.group(2) }
+    def downgrade(self, match):
+        element = ET.fromstring(match.group(0))
+
+        # Only process this heading if 'headdown="1"' (or missing...)
+        if element.attrib.get('headdown', 1) == 1:
+            # For all headings, increase their heading number by `offset`.
+            # If the new heading number is > 6, use 6 instead.
+            element.tag = 'h%d' % min(6, int(match.group(1))+self.offset)
+
+        return ET.tostring(element, encoding="unicode")
 
 class DowngradeHeadingsExtension(Extension):
     """ Setup the extension for usage. """