code: def update(self, *names: Any) -> None:
          
          _names = [str(name) for name in names]
          self._check_keywords(_names)
          super().update(_names)
docs: Before updating, the given names are checked to be valid
          variable identifiers.
  
          >>> from hydpy.core.devicetools import Keywords
          >>> keywords = Keywords('first_keyword', 'second_keyword',
          ...                     'keyword_3', 'keyword_4',
          ...                     'keyboard')
          >>> keywords.update('test_1', 'test 2')   # doctest: +ELLIPSIS
          Traceback (most recent call last):
          ...
          ValueError: While trying to add the keyword `test 2` to device ?, \
  the following error occurred: The given name string `test 2` does not \
  define a valid variable identifier.  ...
  
          Note that even the first string (`test1`) is not added due to the
          second one (`test 2`) being invalid.
  
          >>> keywords
          Keywords("first_keyword", "keyboard", "keyword_3", "keyword_4",
                   "second_keyword")
  
          After correcting the second string, everything works fine:
  
          >>> keywords.update('test_1', 'test_2')
          >>> keywords
          Keywords("first_keyword", "keyboard", "keyword_3", "keyword_4",
                   "second_keyword", "test_1", "test_2")