Find the highest level heading (i.e. having the least '#'s)
        in a Markdown string.

        :param content: Markdown content

        :returns: Maximum heading level detected; if no heading is found, 0 is returned

def _find_top_heading_level(self, content: str) -> int:
        '''Find the highest level heading (i.e. having the least '#'s)
        in a Markdown string.

        :param content: Markdown content

        :returns: Maximum heading level detected; if no heading is found, 0 is returned
        '''

        result = float('inf')

        for heading in self._heading_pattern.finditer(content):
            heading_level = len(heading.group('hashes'))

            if heading_level < result:
                result = heading_level

            self.logger.debug(f'Maximum heading level: {result}')

        return result if result < float('inf') else 0