The DDIF input converter converts a compound document DDIF input
    file to an intermediate format that is then converted to the
    specified output file format. If the DDIF input file is a newer
    version of the DDIF grammar than that understood by the DDIF
    input converter, data represented by the new grammar elements is
    lost.

    The DDIF input converter does not resolve external references,
    although the converter kernel can if requested by the output
    converter. A document syntax error in the DDIF input file causes
    a fatal input processing error and conversion stops.