def references2marc(self, key, value):
    """Populate the ``999C5`` MARC field."""
    reference = value.get('reference', {})

    pids = force_list(reference.get('persistent_identifiers'))
    a_values = ['doi:' + el for el in force_list(reference.get('dois'))]
    a_values.extend(['hdl:' + el['value'] for el in pids if el.get('schema') == 'HDL'])
    a_values.extend(['urn:' + el['value'] for el in pids if el.get('schema') == 'URN'])

    external_ids = force_list(reference.get('external_system_identifiers'))
    u_values = force_list(get_value(reference, 'urls.value'))
    u_values.extend(CDS_RECORD_FORMAT.format(el['value']) for el in external_ids if el.get('schema') == 'CDS')
    u_values.extend(ADS_RECORD_FORMAT.format(el['value']) for el in external_ids if el.get('schema') == 'ADS')

    authors = force_list(reference.get('authors'))
    e_values = [el['full_name'] for el in authors if el.get('inspire_role') == 'editor']
    h_values = [el['full_name'] for el in authors if el.get('inspire_role') != 'editor']

    r_values = force_list(reference.get('report_numbers'))
    if reference.get('arxiv_eprint'):
        arxiv_eprint = reference['arxiv_eprint']
        r_values.append('arXiv:' + arxiv_eprint if is_arxiv_post_2007(arxiv_eprint) else arxiv_eprint)

    if reference.get('publication_info'):
        reference['publication_info'] = convert_new_publication_info_to_old([reference['publication_info']])[0]
    journal_title = get_value(reference, 'publication_info.journal_title')
    journal_volume = get_value(reference, 'publication_info.journal_volume')
    page_start = get_value(reference, 'publication_info.page_start')
    page_end = get_value(reference, 'publication_info.page_end')
    artid = get_value(reference, 'publication_info.artid')
    s_value = build_pubnote(journal_title, journal_volume, page_start, page_end, artid)

    m_value = ' / '.join(force_list(reference.get('misc')))

    return {
        '0': get_recid_from_ref(value.get('record')),
        '9': 'CURATOR' if value.get('legacy_curated') else None,
        'a': a_values,
        'b': get_value(reference, 'publication_info.cnum'),
        'c': reference.get('collaborations'),
        'e': e_values,
        'h': h_values,
        'i': reference.get('isbn'),
        'k': reference.get('texkey'),
        'm': m_value,
        'o': reference.get('label'),
        'p': get_value(reference, 'imprint.publisher'),
        'q': get_value(reference, 'publication_info.parent_title'),
        'r': r_values,
        's': s_value,
        't': get_value(reference, 'title.title'),
        'u': u_values,
        'x': get_value(value, 'raw_refs.value'),
        'y': get_value(reference, 'publication_info.year'),
        'z': 1 if value.get('curated_relation') else 0,
    }