import re


def parse_bookmark(string):
    """
    Parse bookmark string

    :param string: line of the bookmarks file representing an html element
    :return: if the line is a bookmark return the href attribute; else None
    """
    match = re.search(r'<A HREF=.+?"', string)
    if match:
        return match.group(0).split('"')[1]
    else:
        return None