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