anchor.diff:  
               match rResult, sResult with
               | Choice2Of2 rErrors, Choice2Of2 sErrors ->
  -                return Choice2Of2 (rErrors @ sErrors)
  +                return Choice2Of2 (rErrors ++ sErrors)
               | (Choice2Of2 _ as err), Choice1Of2 _
               | Choice1Of2 _, (Choice2Of2 _ as err) ->
                   return err
  
positive.code: 
              match rResult, sResult with
              | Choice2Of2 rErrors, Choice2Of2 sErrors ->
                  return Choice2Of2 (rErrors @ sErrors)
              | (Choice2Of2 _ as err), Choice1Of2 _
              | Choice1Of2 _, (Choice2Of2 _ as err) ->
                  return err
  
negative.code:                 match UnicodeCharSet.ofAbbreviation abbrev with
                  | None ->
                      return
                          sprintf "Unknown or invalid Unicode category specified. (Category = %s)" abbrev
                          |> LazyList.singleton
                          |> Choice2Of2
  
                  | Some charSet ->
  