docs: def prompt_layer_selection(self, node, layers):
          """Ask user what to do when an old node is contained in more than one layer.
          Possible answers are:
              * use default layer (default answer if pressing enter)
              * choose layer
              * discard node
          """
          valid = {
              "default": "default",
              "def": "default",
              "discard": "discard",
              "dis": "discard",
          }
          question = """Cannot automatically determine layer for node "%s" because there \
  are %d layers available in that area, what do you want to do?\n\n""" % (node.name, len(layers))
  
          available_layers = ""
          for layer in layers:
              available_layers += "%d (%s)\n" % (layer.id, layer.name)
              valid[str(layer.id)] = layer.id
  
          prompt = """\
  choose (enter the number of) one of the following layers:
  %s
  "default"    use default layer (if no default layer specified in settings node will be discarded)
  "discard"    discard node
  
  (default action is to use default layer)\n\n""" % available_layers
  
          sys.stdout.write(question + prompt)
  
          while True:
              if self.options.get('noinput') is True:
                  answer = 'default'
                  break
  
              answer = raw_input().lower()
              if answer == '':
                  answer = "default"
  
              if answer in valid:
                  answer = valid[answer]
                  break
              else:
                  sys.stdout.write("Please respond with one of the valid answers\n")
  
          sys.stdout.write("\n")
          return answer