epub converter: add internal links processing 6a

src/html_epub_preprocessor.py

@@ -114,6 +114,7 @@ def _process_lists(body_tag):
 
 
 def clean_headings_content(content: Tag, title: str):
+    title = title.lower()
     for child in content.contents:
         if isinstance(child, NavigableString):
             text = child
@@ -122,6 +123,7 @@ def clean_headings_content(content: Tag, title: str):
         if text and re.sub(r'([\n\t\xa0])', '', text):
             text = re.sub(r'([\n\t\xa0])', ' ', text)
             text = re.sub(r' +', ' ', text).strip()
+            text = text.lower()
             if title == text:
                 child.extract()
             elif (title in text) and (child.name in ['h1', 'h2', 'h3']):