'The charset from the content type.'

@cached_property
def charset(self):

    header = self.environ.get('CONTENT_TYPE')
    if header:
        (ct, options) = parse_options_header(header)
        charset = options.get('charset')
        if charset:
            if is_known_charset(charset):
                return charset
            return self.unknown_charset(charset)
    return self.default_charset
