def split_tagblock(nmea):
    """
    Split off the tagblock from the rest of the message

    Note that if the nmea is a concatenated multipart message then only the tagblock of
    the first message will be split off
    """
    tagblock = ''
    if nmea.startswith("\\") and not nmea.startswith("\\!"):
        tagblock, nmea = nmea[1:].split("\\", 1)
    return tagblock, nmea