diff --git a/cpdfprinttree.mli b/cpdfprinttree.mli
index fad421c..b1fb691 100644
--- a/cpdfprinttree.mli
+++ b/cpdfprinttree.mli
@@ -1,5 +1,7 @@
 (** Print trees *)
 
+(** Print a tree to a buffer. *)
 val to_buffer : ?line_prefix: string -> get_name: ('a -> string) -> get_children: ('a -> 'a list) -> Buffer.t -> 'a -> unit
 
+(** Print a tree to a string. *)
 val to_string : ?line_prefix: string -> get_name: ('a -> string) -> get_children: ('a -> 'a list) -> 'a -> string
diff --git a/cpdfua.mli b/cpdfua.mli
index e097a2d..4813a92 100644
--- a/cpdfua.mli
+++ b/cpdfua.mli
@@ -1,16 +1,25 @@
 (** PDF/UA *)
+
+(** Print matterhorn test results ("" = all tests) *)
 val test_matterhorn_print : Pdf.t -> string -> unit
 
+(** Return JSON results of a matterhorn test ("" = all tests *) 
 val test_matterhorn_json : Pdf.t -> string -> Cpdfyojson.Safe.t
 
+(** Mark PDF as PDF/UA-1 compliant. *)
 val mark : Pdf.t -> unit
 
+(** Mark PDF as PDF/UA-2 compliant. *)
 val mark2 : int -> Pdf.t -> unit
 
+(** Remove any PDF/UA-* marker *)
 val remove_mark : Pdf.t -> unit
 
+(** Print the structure tree to standard output, graphically. *)
 val print_struct_tree : Pdf.t -> unit
 
+(** Extract structure tree to JSON *)
 val extract_struct_tree : Pdf.t -> Cpdfyojson.Safe.t
 
+(** Reapply an edited JSON structure tree to its PDF. *)
 val replace_struct_tree : Pdf.t -> Cpdfyojson.Safe.t -> unit