def is_start_byte(b: int) -> bool:
    """Check if b is a start character byte in utf8
       See https://en.wikipedia.org/wiki/UTF-8
       for encoding details
    Args:
        b (int): a utf8 byte

    Returns:
        bool: whether or not b is a valid starting byte
    """

    # a non-start char has encoding 10xxxxxx
    return (b >> 6) != 2