docs: function resolveBlockDir(
    str: string,
    fallback: ?BidiDirection,
  ): BidiDirection {
    fallback = fallback || UnicodeBidiDirection.NEUTRAL;
    if (!str.length) {
      return fallback;
    }
    const blockDir = firstStrongCharDir(str);
    return (blockDir === UnicodeBidiDirection.NEUTRAL) ? fallback : blockDir;
  }