docs: def parse_content_type(content_type):
      """
      Return a tuple of content type and charset.
  
      :param content_type: A string describing a content type.
      """
      if '; charset=' in content_type:
          return tuple(content_type.split('; charset='))
      else:
          if 'text' in content_type:
              encoding = 'ISO-8859-1'
          else:
              try:
                  format = formats.find_by_content_type(content_type)
              except formats.UnknownFormat:
                  encoding = 'ISO-8859-1'
              else:
                  encoding = format.default_encoding or 'ISO-8859-1'
  
          return (content_type, encoding)