docs: def _env_filenames(filenames, env):
      """
      Extend filenames with ennv indication of environments.
  
      :param list filenames: list of strings indicating filenames
      :param str env: environment indicator
  
      :returns: list of filenames extended with environment version
      :rtype: list
      """
      env_filenames = []
      for filename in filenames:
          filename_parts = filename.split('.')
          filename_parts.insert(1, env)
          env_filenames.extend([filename, '.'.join(filename_parts)])
  
      return env_filenames