code: def _tag_matches_pattern(tag, pattern):
      
      for char1, char2 in zip(tag, pattern):
          if char2 not in ('%', char1):
              return False
      return True
docs: Return true if MARC 'tag' matches a 'pattern'.
  
      'pattern' is plain text, with % as wildcard
  
      Both parameters must be 3 characters long strings.
  
      .. doctest::
  
          >>> _tag_matches_pattern("909", "909")
          True
          >>> _tag_matches_pattern("909", "9%9")
          True
          >>> _tag_matches_pattern("909", "9%8")
          False
  
      :param tag: a 3 characters long string
      :param pattern: a 3 characters long string
      :return: False or True