docs: def _comment_type_from_line(line):
      """Return the "comment header" (' * ', '# ', 'rem ', '// ', '/* ').
  
      This header goes before the content of a start of the
      line in a replacement.
      """
      regex = re.compile(r"^{0}".format(_ALL_COMMENT))
      match = regex.match(line)
      if match:
          return "{0} ".format(line[match.start():match.end()])
  
      raise RuntimeError("Unable to find comment header for {0}".format(line))