REGEXP_FILE
  RegExpPatternImpl: <((a))>
    RegExpBranchImpl: <((a))>
      RegExpGroupImpl: <((a))>
        PsiElement(GROUP_BEGIN)('(')
        RegExpPatternImpl: <(a)>
          RegExpBranchImpl: <(a)>
            RegExpGroupImpl: <(a)>
              PsiElement(GROUP_BEGIN)('(')
              RegExpPatternImpl: <a>
                RegExpBranchImpl: <a>
                  RegExpCharImpl: <a>
                    PsiElement(CHARACTER)('a')
              PsiElement(GROUP_END)(')')
        PsiElement(GROUP_END)(')')