List of all lowercased hashtags (without preceeding #) that occur in the Post's caption.

def caption_hashtags(self) -> List[str]:
        """List of all lowercased hashtags (without preceeding #) that occur in the Post's caption."""
        if not self.caption:
            return []
        # This regular expression is from jStassen, adjusted to use Python's \w to support Unicode
        # http://blog.jstassen.com/2016/03/code-regex-for-instagram-username-and-hashtags/
        hashtag_regex = re.compile(r"(?:#)(\w(?:(?:\w|(?:\.(?!\.))){0,28}(?:\w))?)")
        return re.findall(hashtag_regex, self.caption.lower())