checkArgument(ascii().matchesAllOf(value), "parameter values must be ASCII: %s", value);
    return CHARSET_ATTRIBUTE.equals(attribute) ? Ascii.toLowerCase(value) : value;
  }

  /**
   * Parses a media type from its string representation.
   *
   * @throws IllegalArgumentException if the input is not parsable
   */
  @CanIgnoreReturnValue // TODO(b/219820829): consider removing