anchor.diff:      | _ -> None
   
   let err_exn exn =
  +    if exn = Stop then ()
  +    else
       match issue_of_exn exn with
       | Some issue -> add_one issue
       | None -> raise exn
  
positive.code: exception Err of string
  exception Error of string * Range.range
  exception Warning of string * Range.range
  
  (* Raised when an empty fragment is parsed *)
  exception Empty_frag
  
negative.code: let handleable = function
    | Error _
    | NYI _
    | Stop
    | Err _ -> true
    | _ -> false
  
  let stop_if_err () =
      if get_err_count () > 0
      then raise Stop
  