docs: def exists(self, index):
          """Checks whether :index: exists in the Model.
  
          :index: Index to look for.
          :returns: True if :index: exists in the Model, False otherwise.
  
          """
          data = self.data
          try:
              for c in self._split(index):
                  i = int(c) - 1
                  data = data[i][4]
          except Exception:
              return False
          return True