val dtd_dir : string lazy_t (* DTDs' root directory *)
val servers_file : string lazy_t (* servers.txt file *)
val port : int lazy_t (* port on which getter listens *)
-val dtd_base_url : string lazy_t (* base URL for DTD downloading *)
+val dtd_base_urls : string list lazy_t (* base URLs for document patching *)
(* {2 derived data} *)