def get_float_relative(strings: Sequence[str],
                       prefix1: str,
                       delta: int,
                       prefix2: str,
                       ignoreleadingcolon: bool = False) -> Optional[float]:
    """
    Fetches a float parameter via :func:`get_string_relative`.
    """
    return get_float_raw(get_string_relative(
        strings, prefix1, delta, prefix2,
        ignoreleadingcolon=ignoreleadingcolon))