docs: def add_field(self, fieldname, fieldspec=whoosh_module_fields.TEXT):
      """Add a field in the index of the model.
  
      Args:
          fieldname (Text): This parameters register a new field in specified model.
          fieldspec (Name, optional): This option adds various options as were described before.
  
      Returns:
          TYPE: The new schema after deleted is returned.
      """
      self._whoosh.add_field(fieldname, fieldspec)
      return self._whoosh.schema