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