def _validate_magic_line(line):
    """For NRRD files, the first four characters are always "NRRD", and
    remaining characters give information about the file format version

    >>> _validate_magic_line('NRRD0005')
    8
    >>> _validate_magic_line('NRRD0006')
    Traceback (most recent call last):
        ...
    NrrdError: NRRD file version too new for this library.
    >>> _validate_magic_line('NRRD')
    Traceback (most recent call last):
        ...
    NrrdError: Invalid NRRD magic line: NRRD
    """

    if not line.startswith('NRRD'):
        raise NRRDError('Invalid NRRD magic line. Is this an NRRD file?')

    try:
        version = int(line[4:])
        if version > 5:
            raise NRRDError('Unsupported NRRD file version (version: %i). This library only supports v%i and below.'
                            % (version, 5))
    except ValueError:
        raise NRRDError('Invalid NRRD magic line: %s' % line)

    return len(line)
For NRRD files, the first four characters are always "NRRD", and
    remaining characters give information about the file format version

    >>> _validate_magic_line('NRRD0005')
    8
    >>> _validate_magic_line('NRRD0006')
    Traceback (most recent call last):
        ...
    NrrdError: NRRD file version too new for this library.
    >>> _validate_magic_line('NRRD')
    Traceback (most recent call last):
        ...
    NrrdError: Invalid NRRD magic line: NRRD