private void parseProlog() {
    final PsiBuilder.Marker prolog = mark();
    while (true) {
      final IElementType tt = token();
      if (tt == XML_PI_START) {
        parseProcessingInstruction();
      }
      else if (tt == XML_DOCTYPE_START) {
        parseDoctype();
      }
      else if (isCommentToken(tt)) {
        parseComment();
      }
      else if (tt == XML_REAL_WHITE_SPACE) {
        advance();
      }
      else {
        break;
      }
    }
    prolog.done(XML_PROLOG);
  }
private void parseProlog()