code: def grfcbk_strlen(args):
      
      if not args[0]:
          return None
      if isinstance(args[0], list):
          return [len(x) for x in args[0]]
      return len(args[0])
docs: Grammar rule function callback: **strlen**. This function will measure the
      string length of all subitems of the first item in argument list.
  
      :param list args: List of function arguments.
      :return: Length of all subitems of the first item in argument list.
      :rtype: int or list