REGEXP_FILE
  RegExpPatternImpl: <abc\x>
    RegExpBranchImpl: <abc\x>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')
      RegExpCharImpl: <\x>
        PsiElement(BAD_HEX_VALUE)('\x')