import re


def is_relative(url: str) -> bool:
    """
        Returns whether given URL is relative.
    """
    if url == "":
        return False

    # https://stackoverflow.com/a/31991870/1907830
    absolute = bool(re.match(r'(?:^[a-z][a-z0-9+.-]*:|\/\/)', url))
    # absolute = bool(re.match('(?:^[a-z][a-z0-9+.-]*:|\/\/)', url))
    hashtag = url[0] == '#'
    return not absolute and not hashtag