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