def validate_fen_board(fen: str) ->bool:
    """Check whether the board portion of a given Forsyth-Edwards Notation is
    valid.

    :param fen: Board portion of Forsyth-Edwards Notation.
    :return: Whether *fen* is valid.
    """
    fen = fen.split()[0]
    chunks = fen.split('/')
    file_length = len(chunks)
    if file_length != 8:
        return False
    for chunk in chunks:
        rank_length = 0
        for char in chunk:
            if char.isnumeric() and char != '0':
                rank_length += int(char)
            elif char.lower() in 'kqrbnp':
                rank_length += 1
            else:
                return False
        if rank_length != 8:
            return False
    return True
