def METHOD_NAME(n_root, filebase):
    # oblivion and Fallout 3 furniture markers
    if bpy.context.scene.niftools_scene.game in ('OBLIVION', 'FALLOUT_3', 'SKYRIM') and filebase[:15].lower() == 'furnituremarker':
        # exporting a furniture marker for Oblivion/FO3
        try:
            furniturenumber = int(filebase[15:])
        except ValueError:
            raise io_scene_niftools.utils.logging.NifError(f"Furniture marker has invalid number ({filebase[15:]}).\n"
                                     f"Name your file 'furnituremarkerxx.nif' where xx is a number between 00 and 19.")
        # create furniture marker block
        furnmark = block_store.create_block("BSFurnitureMarker")
        furnmark.name = "FRN"
        furnmark.num_positions = 1
        furnmark.reset_field("positions")
        furnmark.positions[0].position_ref_1 = furniturenumber
        furnmark.positions[0].position_ref_2 = furniturenumber
        # create extra string data sgoKeep
        sgokeep = block_store.create_block("NiStringExtraData")
        sgokeep.name = "UPB"  # user property buffer
        sgokeep.string_data = "sgoKeep=1 ExportSel = Yes"  # Unyielding = 0, sgoKeep=1ExportSel = Yes
        # add extra blocks
        n_root.add_extra_data(furnmark)
        n_root.add_extra_data(sgokeep)