REGEXP_FILE
  RegExpPatternImpl: <a{}>
    RegExpBranchImpl: <a{}>
      RegExpClosureImpl: <a{}>
        RegExpCharImpl: <a>
          PsiElement(CHARACTER)('a')
        RegExpQuantifierImpl: <{}>
          PsiElement(LBRACE)('{')
          PsiErrorElement:Number expected
            <empty list>
          PsiElement(RBRACE)('}')