docs: def resolve_mode(self, name):
          """
          From given mode name, return mode file path from
          ``settings.CODEMIRROR_MODES`` map.
  
          Arguments:
              name (string): Mode name.
  
          Raises:
              KeyError: When given name does not exist in
                  ``settings.CODEMIRROR_MODES``.
  
          Returns:
              string: Mode file path.
          """
          if name not in settings.CODEMIRROR_MODES:
              msg = ("Given config name '{}' does not exists in "
                     "'settings.CODEMIRROR_MODES'.")
              raise UnknowModeError(msg.format(name))
  
          return settings.CODEMIRROR_MODES.get(name)