REGEXP_FILE
  RegExpPatternImpl: <a[+*?]b>
    RegExpBranchImpl: <a[+*?]b>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpClassImpl: <[+*?]>
        PsiElement(CLASS_BEGIN)('[')
        RegExpCharImpl: <+>
          PsiElement(CHARACTER)('+')
        RegExpCharImpl: <*>
          PsiElement(CHARACTER)('*')
        RegExpCharImpl: <?>
          PsiElement(CHARACTER)('?')
        PsiElement(CLASS_END)(']')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')