docs: def max_substring(words, position=0, _last_letter=''):
      """Finds max substring shared by all strings starting at position
  
      Args:
  
          words (list): list of unicode of all words to compare
  
          position (int): starting position in each word to begin analyzing
                          for substring
  
          _last_letter (unicode): last common letter, only for use
                                  internally unless you really know what
                                  you are doing
  
      Returns:
          unicode: max str common to all words
  
      Examples:
          .. code-block:: Python
  
              >>> max_substring(['aaaa', 'aaab', 'aaac'])
              'aaa'
              >>> max_substring(['abbb', 'bbbb', 'cbbb'], position=1)
              'bbb'
              >>> max_substring(['abc', 'bcd', 'cde'])
              ''
      """
  
      # If end of word is reached, begin reconstructing the substring
      try:
          letter = [word[position] for word in words]
      except IndexError:
          return _last_letter
  
      # Recurse if position matches, else begin reconstructing the substring
      if all(l == letter[0] for l in letter) is True:
          _last_letter += max_substring(words, position=position + 1,
                                        _last_letter=letter[0])
          return _last_letter
      else:
          return _last_letter