Fix HTML.is_document mistakenly pointing at is_root instead

src/plugin_api.ml

@@ -902,7 +902,7 @@ struct
         (* Node tests. *)
         "is_element", V.efunc (V.option Map.html **->> V.bool) (fun n -> match n with None -> false | Some n -> Html.is_element n);
         "is_root", V.efunc (V.option Map.html **->> V.bool) (fun n -> match n with None -> false | Some n -> Html.is_root n);
-        "is_document", V.efunc (V.option Map.html **->> V.bool) (fun n -> match n with None -> false | Some n -> Html.is_root n);
+        "is_document", V.efunc (V.option Map.html **->> V.bool) (fun n -> match n with None -> false | Some n -> Html.is_document n);
 
         (* High-level convenience functions. *)
         "get_heading_level", V.efunc (V.option Map.html **->> V.option V.int) Html.get_heading_level;