def _writeMzmlIndexList(xmlWriter, spectrumIndexList, chromatogramIndexList):
    """ #TODO: docstring

    :param xmlWriter: #TODO: docstring
    :param spectrumIndexList: #TODO: docstring
    :param chromatogramIndexList: #TODO: docstring
    """
    counts = 0
    if spectrumIndexList:
        counts += 1
    if chromatogramIndexList:
        counts += 1
    if counts == 0:
        return None
    #Create indexList node
    xmlIndexList = xmlWriter.element('indexList', {'count': str(counts)})
    xmlIndexList.__enter__()
    xmlWriter.write('\n')

    _writeIndexListElement(xmlWriter, 'spectrum', spectrumIndexList)
    _writeIndexListElement(xmlWriter, 'chromatogram', chromatogramIndexList)

    #Close indexList node
    xmlIndexList.__exit__(None, None, None)
    xmlWriter.write('\n')