REGEXP_FILE
  RegExpPatternImpl: <(a|b)c*d>
    RegExpBranchImpl: <(a|b)c*d>
      RegExpGroupImpl: <(a|b)>
        PsiElement(GROUP_BEGIN)('(')
        RegExpPatternImpl: <a|b>
          RegExpBranchImpl: <a>
            RegExpCharImpl: <a>
              PsiElement(CHARACTER)('a')
          PsiElement(UNION)('|')
          RegExpBranchImpl: <b>
            RegExpCharImpl: <b>
              PsiElement(CHARACTER)('b')
        PsiElement(GROUP_END)(')')
      RegExpClosureImpl: <c*>
        RegExpCharImpl: <c>
          PsiElement(CHARACTER)('c')
        RegExpQuantifierImpl: <*>
          PsiElement(STAR)('*')
      RegExpCharImpl: <d>
        PsiElement(CHARACTER)('d')