REGEXP_FILE
  RegExpPatternImpl: <ab?c>
    RegExpBranchImpl: <ab?c>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpClosureImpl: <b?>
        RegExpCharImpl: <b>
          PsiElement(CHARACTER)('b')
        RegExpQuantifierImpl: <?>
          PsiElement(QUEST)('?')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')