diff --git a/src/lib/biocaml_gff.ml b/src/lib/biocaml_gff.ml
index 9a0f23d..de4eda8 100644
--- a/src/lib/biocaml_gff.ml
+++ b/src/lib/biocaml_gff.ml
@@ -31,8 +31,15 @@ let module_error e = Error (`gff e)
 
 module Tags = struct
 
-  type t = [ `version of [`two | `three] | `pedantic ] list with sexp
-  let default = [`version `three; `pedantic]
+  type t = {
+    version: [`two | `three];
+    allow_empty_lines: bool;
+    sharp_comments: bool;
+  }
+  with sexp
+
+  let default =
+    {version = `three; allow_empty_lines = false; sharp_comments = true}
 
 
   let to_string t = sexp_of_t t |> Sexplib.Sexp.to_string
@@ -198,25 +205,23 @@ module Transform = struct
       output_error (`wrong_row (pos, s))
     end
 
-  let rec next ?(pedantic=true) ?(sharp_comments=true) ?(version=`three) p =
+  let rec next ~tags  p =
     let open Biocaml_lines.Buffer in
     let open Result in
     match (next_line p :> string option) with
     | None -> `not_ready
     | Some "" ->
-      if pedantic
+      if tags.Tags.allow_empty_lines
       then output_error (`empty_line (current_position p))
-      else next ~pedantic ~sharp_comments ~version p
-    | Some l when sharp_comments && String.(is_prefix (strip l) ~prefix:"#") ->
+      else next ~tags p
+    | Some l when
+        tags.Tags.sharp_comments && String.(is_prefix (strip l) ~prefix:"#") ->
       output_ok (`comment String.(sub l ~pos:1 ~len:(length l - 1)))
-    | Some l -> parse_row ~version (current_position p) l
+    | Some l -> parse_row ~version:tags.Tags.version (current_position p) l
 
-  let string_to_item ?filename ?(tags=Tags.default) () =
+  let string_to_item ?filename ~tags () =
     let name = sprintf "gff_parser:%s" Option.(value ~default:"<>" filename) in
-    let pedantic = List.mem tags  `pedantic in
-    let version =
-      List.find_map tags (function `version v -> Some v | _ -> None) in
-    let next = next ~pedantic ?version in
+    let next = next ~tags in
     Biocaml_lines.Transform.make_merge_error ~name ?filename ~next ()
 
   let item_to_string_pure version = (function
@@ -248,20 +253,18 @@ module Transform = struct
     ] ^ "\n"
   )
 
-  let item_to_string ?(tags=Tags.default) () =
-    let version =
-      List.find_map tags (function `version v -> Some v | _ -> None)
-      |! Option.value ~default:`three in
+  let item_to_string ~tags () =
     Biocaml_transform.of_function ~name:"gff_to_string"
-      (item_to_string_pure version)
+      (item_to_string_pure tags.Tags.version)
 
 end
 
 exception Error of  Error.t
 let error_to_exn e = Error e
 
-let in_channel_to_item_stream ?(buffer_size=65536) ?filename ?tags inp =
-  let x = Transform.string_to_item ?tags ?filename () in
+let in_channel_to_item_stream
+    ?(buffer_size=65536) ?filename ?(tags=Tags.default) inp =
+  let x = Transform.string_to_item ~tags ?filename () in
   Biocaml_transform.(in_channel_strings_to_stream inp x ~buffer_size)
 
 let in_channel_to_item_stream_exn ?buffer_size ?tags inp =
@@ -269,7 +272,4 @@ let in_channel_to_item_stream_exn ?buffer_size ?tags inp =
     (in_channel_to_item_stream ?buffer_size ?tags inp)
 
 let item_to_string ?(tags=Tags.default) item =
-  let version =
-    List.find_map tags (function `version v -> Some v | _ -> None)
-    |! Option.value ~default:`three in
-  Transform.item_to_string_pure version item
+  Transform.item_to_string_pure tags.Tags.version item
diff --git a/src/lib/biocaml_gff.mli b/src/lib/biocaml_gff.mli
index 875ceff..0df4fb5 100644
--- a/src/lib/biocaml_gff.mli
+++ b/src/lib/biocaml_gff.mli
@@ -70,11 +70,16 @@ end
 
 module Tags: sig
 
-  type t = [ `version of [`two | `three] | `pedantic ] list
+  type t = {
+    version: [`two | `three];
+    allow_empty_lines: bool;
+    sharp_comments: bool;
+  }
   (** Additional format-information tags (c.f. {!Biocaml_tags}). *)
 
   val default: t
-  (** Default tags for a random Gff file: [[`version `three; `pedantic]]. *)
+  (** Default tags for a random Gff file:
+      [{version = `three; allow_empty_lines = false; sharp_comments = true}]. *)
 
   val of_string: string ->
     (t, [> `gff of [> `tags_of_string of exn ] ]) Core.Result.t
@@ -114,12 +119,12 @@ module Transform: sig
 
   val string_to_item:
     ?filename:string ->
-    ?tags: Tags.t ->
+    tags: Tags.t ->
     unit ->
     (string, (item, [> Error.parsing]) Core.Result.t) Biocaml_transform.t
   (** Create a parsing [Biocaml_transform.t] for a given version. *)
 
-  val item_to_string: ?tags: Tags.t -> unit ->
+  val item_to_string: tags: Tags.t -> unit ->
     (item, string) Biocaml_transform.t
   (** Create a printer for a given version. *)
 
diff --git a/src/lib/biocaml_track.ml b/src/lib/biocaml_track.ml
index 12e4237..341e9eb 100644
--- a/src/lib/biocaml_track.ml
+++ b/src/lib/biocaml_track.ml
@@ -154,9 +154,9 @@ module Transform = struct
 
   type gff_parse_error = [Error.parsing | Gff.Error.parsing]
   type gff_t = [track | Gff.item]
-  let string_to_gff ?filename ?tags () =
+  let string_to_gff ?filename ~tags () =
     let gff = Gff.Transform.string_to_item ?filename () in
-    embed_parser  ?filename gff
+    embed_parser  ?filename (gff ~tags)
       ~reconstruct:(function
       | `bypassed (Ok f) -> Ok (f :> gff_t)
       | `bypassed (Error f) -> Error (f :> [> gff_parse_error])
@@ -192,8 +192,8 @@ module Transform = struct
       | `comment _ | `track _ | `browser _ as x -> `left x
       | #Wig.item as y -> `right y)
 
-  let gff_to_string ?tags () =
-    let gff = Gff.Transform.item_to_string ?tags () in
+  let gff_to_string ~tags () =
+    let gff = Gff.Transform.item_to_string ~tags () in
     make_printer gff ()
       ~split:(function
       | `comment _ | `track _ | `browser _ as x -> `left x
diff --git a/src/lib/biocaml_track.mli b/src/lib/biocaml_track.mli
index a4b327c..1d8d173 100644
--- a/src/lib/biocaml_track.mli
+++ b/src/lib/biocaml_track.mli
@@ -110,13 +110,13 @@ module Transform: sig
     ([ t | Biocaml_wig.item ], string) Biocaml_transform.t
   (** Create a printer for track files containing WIG lines. *)
 
-  val string_to_gff: ?filename:string -> ?tags: Biocaml_gff.Tags.t -> unit ->
+  val string_to_gff: ?filename:string -> tags: Biocaml_gff.Tags.t -> unit ->
     (string,
      ([t | Biocaml_gff.item], [> Error.parsing | Biocaml_gff.Error.parsing])
        Core.Result.t) Biocaml_transform.t
   (** Create a composite parser for UCSC GFF files.  *)
 
-  val gff_to_string: ?tags: Biocaml_gff.Tags.t -> unit ->
+  val gff_to_string: tags: Biocaml_gff.Tags.t -> unit ->
     ([ t | Biocaml_gff.item ], string) Biocaml_transform.t
   (** Create a printer for track files containing GFF lines. *)
 
@@ -132,4 +132,3 @@ module Transform: sig
   (** Create a printer for track files containing Bed(Graph) lines. *)
 
 end
-
diff --git a/src/tests/test_gff.ml b/src/tests/test_gff.ml
index 6c74b40..dc3c25f 100644
--- a/src/tests/test_gff.ml
+++ b/src/tests/test_gff.ml
@@ -3,7 +3,7 @@ open Biocaml_internal_pervasives
 open Biocaml
 
 let test_parser () =
-  let transfo = Gff.Transform.string_to_item () in
+  let transfo = Gff.Transform.string_to_item ~tags:Gff.Tags.default () in
   let test_line l f =
     let joined = (String.concat ~sep:"\t" l) in
     Transform.feed transfo (joined ^ "\n");
@@ -27,7 +27,7 @@ let test_parser () =
              pos = (42, 43); score = Some 2.; strand = `plus;
              phase = Some 2;
              attributes = ["k", ["v"; "v v"]; "big k", ["annoying v"]]});
-  
+
   test_line ["\"big\\tC style\""; "some";  "s"; "42"; "43"; "2."; "+"]
     (function | `output (Error (`wrong_row (_, _))) -> true | _ -> false);
 
@@ -56,7 +56,10 @@ let test_parser () =
             "some=string;djf"]
     (function | `output (Error (`wrong_attributes (_, _))) -> true | _ -> false);
 
-  let transfo = Gff.Transform.string_to_item ~tags:[`version `two] () in
+  let transfo =
+    let tags =
+      { Gff.Tags.default with Gff.Tags.version = `two; allow_empty_lines = true} in
+    Gff.Transform.string_to_item ~tags () in
   let test_line l f =
     let joined = (String.concat ~sep:"\t" l) in
     Transform.feed transfo (joined ^ "\n");
@@ -73,16 +76,16 @@ let test_parser () =
          pos = (42, 43); score = Some 2.; strand = `plus;
          phase = Some 2; attributes = ["k", ["v"]; "big\tk", ["annoying v"]]});
   ()
-   
+
 let test_printer () =
-  let transfo = Gff.Transform.item_to_string () in
+  let transfo = Gff.Transform.item_to_string ~tags:Gff.Tags.default () in
   let test s item =
     Transform.feed transfo item;
     let res =  Transform.next transfo in
     match res with
     | `output o ->
       if s <> o then eprintf "NOT EQUALS:\n%S\n%S\n%!" s o;
-      assert_equal ~printer:ident s o 
+      assert_equal ~printer:ident s o
     | `not_ready -> assert_bool "not_ready" false
     | `end_of_stream -> assert_bool "end_of_stream" false
   in
@@ -100,14 +103,17 @@ let test_printer () =
              phase = None; attributes = [
                "k", ["v"]; "big k", ["an;no\ting\nv"]
              ]});
-  let transfo = Gff.Transform.item_to_string ~tags:[ `version `two] () in
+  let transfo =
+    let tags =
+      { Gff.Tags.default with Gff.Tags.version = `two; allow_empty_lines = true} in
+    Gff.Transform.item_to_string ~tags () in
   let test s item =
     Transform.feed transfo item;
     let res =  Transform.next transfo in
     match res with
     | `output o ->
       if s <> o then eprintf "NOT EQUALS (version 2):\n%S\n%S\n%!" s o;
-      assert_equal ~printer:ident s o 
+      assert_equal ~printer:ident s o
     | `not_ready -> assert_bool "not_ready" false
     | `end_of_stream -> assert_bool "end_of_stream" false
   in
@@ -120,7 +126,7 @@ let test_printer () =
              ]});
   ()
 
-  
+
 let tests = "GFF" >::: [
   "Parse GFF" >:: test_parser;
   "Print GFF" >:: test_printer;
diff --git a/src/tests/test_track.ml b/src/tests/test_track.ml
index 42478ec..ad75dea 100644
--- a/src/tests/test_track.ml
+++ b/src/tests/test_track.ml
@@ -63,7 +63,7 @@ let test_wig_parser () =
   ()
 
 let test_gff_parser () =
-  let transfo = Track.Transform.string_to_gff () in
+  let transfo = Track.Transform.string_to_gff ~tags:Gff.Tags.default () in
   let test_line l f =
     Transform.feed transfo (l ^ "\n");
     assert_bool l (f (Transform.next transfo))
@@ -130,7 +130,7 @@ let test_wig_printer () =
   ()
 
 let test_gff_printer () =
-  let transfo = Track.Transform.gff_to_string () in
+  let transfo = Track.Transform.gff_to_string ~tags:Gff.Tags.default () in
   let test_line i l =
     Transform.feed transfo i;
     assert_bool l (Transform.next transfo = `output (l ^ "\n"))