   ###
   check_fd: =>
     Logger.log 'problem_check', @answers
-
 
     # If there are no file inputs in the problem, we can fall back on @check
     if $('input:file').length == 0

      if ($(inp).is("input[waitfor]"))
        try
          $(inp).data("waitfor")()
        catch e
          if e.name == "Waitfor Exception"
            alert e.message
          else
            alert "Could not grade your answer. The submission was aborted."
          throw e
    @refreshAnswers()


  ###

  # invalid. To do so, the callee must throw an exception named "Waitfor
  # Exception". This and any other errors or exceptions that arise from the
  # callee are rethrown and abort the submission.
  #
  # In order to use this feature, add a 'data-waitfor' attribute to the input,
  # and specify the function to be called by the check button before sending
  # off @answers
