docs: def natural_keys(text: str) -> List[Union[int, str]]:
      """
      Sort key function.
      Returns text split into string/number parts, for natural sorting; as per
      http://stackoverflow.com/questions/5967500/how-to-correctly-sort-a-string-with-a-number-inside
      
      Example (as per the source above):
          
      .. code-block:: python
      
          >>> from cardinal_pythonlib.sort import natural_keys
          >>> alist=[
          ...     "something1",
          ...     "something12",
          ...     "something17",
          ...     "something2",
          ...     "something25",
          ...     "something29"
          ... ]
          >>> alist.sort(key=natural_keys)
          >>> alist
          ['something1', 'something2', 'something12', 'something17', 'something25', 'something29']
          
      """  # noqa
      return [atoi(c) for c in re.split(r'(\d+)', text)]