code: function firstStrongChar(str: string): ?string {
    const match = REGEX_STRONG.exec(str);
    return match == null ? null : match[0];
  }
docs: Returns the first strong character (has Bidi_Class value of L, R, or AL).
  
  @param str  A text block; e.g. paragraph, table cell, tag
  @return     A character with strong bidi direction, or null if not found