header_with_permalink_pattern = re.compile(r"^(#{1,6}) (.+?)(\s*\{\s*#.*\s*\})\s*$")
code_block3_pattern = re.compile(r"^\s*```")
code_block4_pattern = re.compile(r"^\s*````")


class VisibleTextExtractor(HTMLParser):
    """Extract visible text from a string with HTML tags."""

    def __init__(self):
        super().__init__()
        self.text_parts = []

    def handle_data(self, data):