REGEXP_FILE
  RegExpPatternImpl: <(a+|b)?>
    RegExpBranchImpl: <(a+|b)?>
      RegExpClosureImpl: <(a+|b)?>
        RegExpGroupImpl: <(a+|b)>
          PsiElement(GROUP_BEGIN)('(')
          RegExpPatternImpl: <a+|b>
            RegExpBranchImpl: <a+>
              RegExpClosureImpl: <a+>
                RegExpCharImpl: <a>
                  PsiElement(CHARACTER)('a')
                RegExpQuantifierImpl: <+>
                  PsiElement(PLUS)('+')
            PsiElement(UNION)('|')
            RegExpBranchImpl: <b>
              RegExpCharImpl: <b>
                PsiElement(CHARACTER)('b')
          PsiElement(GROUP_END)(')')
        RegExpQuantifierImpl: <?>
          PsiElement(QUEST)('?')