grf {
 grfid : "ZUU0";
 name : string(STR_GRF_NAME);
 desc : string(STR_GRF_DESCRIPTION);
 version: 1;
 min_compatible_version: 1;
}

item (FEAT_INDUSTRIES, item_industry_coal_mine) {
 property {
  substitute: 00; // coal mine
  override: 00;
 }
 graphics {
  random_prod_change: STORE_PERM(extra_callback_info_1, 1);
 }
}

# nmlc output:
# ERROR: "main.nml", line 16: Unrecognized identifier 'extra_callback_info_1' encountered