protected void parsePattern(PsiBuilder builder) {
    final PsiBuilder.Marker marker = builder.mark();

    parseBranch(builder);

    while (builder.getTokenType() == RegExpTT.UNION) {
      builder.advanceLexer();
      parseBranch(builder);
    }

    marker.done(RegExpElementTypes.PATTERN);
  }
protected void parsePattern(PsiBuilder builder)