val nuprl_dir : string lazy_t (* XMLs' directory for NuPRL*)
val rdf_dir : string lazy_t (* RDFs' directory *)
val dtd_dir : string lazy_t (* DTDs' root directory *)
-val servers_file : string lazy_t (* servers.txt file *)
+val servers_file : string option lazy_t (* servers.txt file *)
val port : int lazy_t (* port on which getter listens *)
val dtd_base_urls : string list lazy_t (* base URLs for document patching *)