How to use the xlsxwriter.relationships.Relationships function in XlsxWriter

def _write_vml_drawing_rels_file(self, worksheet, index):
        # Write the vmlDdrawing .rels files for worksheets with images in
        # headers or footers.

        # Create the drawing .rels dir.
        rels = Relationships()

        for drawing_data in worksheet.vml_drawing_links:
            rels._add_document_relationship(*drawing_data)

        # Create .rels file such as /xl/drawings/_rels/vmlDrawing1.vml.rels.
        rels._set_xml_writer(self._filename('xl/drawings/_rels/vmlDrawing'
                                            + str(index)
                                            + '.vml.rels'))
        rels._assemble_xml_file()

def _write_root_rels_file(self):
        # Write the _rels/.rels xml file.
        rels = Relationships()

        rels._add_document_relationship('/officeDocument', 'xl/workbook.xml')

        rels._add_package_relationship('/metadata/core-properties',
                                       'docProps/core.xml')

        rels._add_document_relationship('/extended-properties',
                                        'docProps/app.xml')

        if self.workbook.custom_properties:
            rels._add_document_relationship('/custom-properties',
                                            'docProps/custom.xml')

        rels._set_xml_writer(self._filename('_rels/.rels'))

        rels._assemble_xml_file()

def _write_workbook_rels_file(self):
        # Write the _rels/.rels xml file.
        rels = Relationships()

        worksheet_index = 1
        chartsheet_index = 1

        for worksheet in self.workbook.worksheets():
            if worksheet.is_chartsheet:
                rels._add_document_relationship('/chartsheet',
                                                'chartsheets/sheet'
                                                + str(chartsheet_index)
                                                + '.xml')
                chartsheet_index += 1
            else:
                rels._add_document_relationship('/worksheet',
                                                'worksheets/sheet'
                                                + str(worksheet_index)
                                                + '.xml')

if worksheet.is_chartsheet:
                continue

            index += 1

            external_links = (worksheet.external_hyper_links +
                              worksheet.external_drawing_links +
                              worksheet.external_vml_links +
                              worksheet.external_table_links +
                              worksheet.external_comment_links)

            if not external_links:
                continue

            # Create the worksheet .rels dirs.
            rels = Relationships()

            for link_data in external_links:
                rels._add_worksheet_relationship(*link_data)

            # Create .rels file such as /xl/worksheets/_rels/sheet1.xml.rels.
            rels._set_xml_writer(self._filename('xl/worksheets/_rels/sheet'
                                                + str(index) + '.xml.rels'))
            rels._assemble_xml_file()

# Write the chartsheet .rels files for links to drawing files.
        index = 0
        for worksheet in self.workbook.worksheets():

            if not worksheet.is_chartsheet:
                continue

            index += 1

            external_links = worksheet.external_drawing_links

            if not external_links:
                continue

            # Create the chartsheet .rels xlsx_dir.
            rels = Relationships()

            for link_data in external_links:
                rels._add_worksheet_relationship(*link_data)

            # Create .rels file such as /xl/chartsheets/_rels/sheet1.xml.rels.
            rels._set_xml_writer(self._filename('xl/chartsheets/_rels/sheet'
                                                + str(index) + '.xml.rels'))
            rels._assemble_xml_file()