def a_filter(tag: str, attr: str, value: str) -> bool:
    """
    filter for <a> html tag.
    Allow "href" and "title" and "target" for some values
    Args:
        tag: html tag : always <a> since used in "a" key of ALLOWED_ATTRIBUTE
        attr: tag attribute
        value: attribute value

    Returns:
        True if keep the attribute
    """
    if attr in ["href", "title"]:
        return True
    if attr == "target" and value in ["_blank", "_top"]:
        return True
    return False