--- /dev/null
+module Span : sig
+ type t
+
+ val of_string : string -> t
+
+ val is_gt_or_eq : t -> t -> bool
+end
+
+type t
+
+val init : t
+
+val diff : t -> t -> Span.t
+
+val to_string : t -> string
+
+val of_string : string -> t
+(** Raises if string is not a number. *)