code: def _write_content_types_stream(phys_writer, parts):
          
          content_types_blob = serialize_part_xml(
              _ContentTypesItem.xml_for(parts)
          )
          phys_writer.write(CONTENT_TYPES_URI, content_types_blob)
docs: Write ``[Content_Types].xml`` part to the physical package with an
          appropriate content type lookup target for each part in *parts*.