REGEXP_FILE
  RegExpPatternImpl: <(abc>
    RegExpBranchImpl: <(abc>
      RegExpGroupImpl: <(abc>
        PsiElement(GROUP_BEGIN)('(')
        RegExpPatternImpl: <abc>
          RegExpBranchImpl: <abc>
            RegExpCharImpl: <a>
              PsiElement(CHARACTER)('a')
            RegExpCharImpl: <b>
              PsiElement(CHARACTER)('b')
            RegExpCharImpl: <c>
              PsiElement(CHARACTER)('c')
        PsiErrorElement:')' expected
          <empty list>