def METHOD_NAME(filename):
    """
    Checks whether a file is CSS waveform data (header) or not.
    :type filename: str
    :param filename: CSS file to be checked.
    :rtype: bool
    :return: ``True`` if a CSS waveform header file.
    """
    # Fixed file format.
    # Tests:
    #  - the length of each line (283 chars)
    #  - two epochal time fields
    #    (for position of dot and if they convert to UTCDateTime)
    #  - supported data type descriptor
    try:
        with open(filename, "rb") as fh:
            lines = fh.readlines()
            # check for empty file
            if not lines:
                return False
            # check every line
            for line in lines:
                assert len(line.rstrip(b"\n\r")) == 283
                assert b"." in line[26:28]
                UTCDateTime(float(line[16:33]))
                assert b"." in line[71:73]
                UTCDateTime(float(line[61:78]))
                assert line[143:145] in DTYPE
    except Exception:
        return False
    return True