REGEXP_FILE
  RegExpPatternImpl: <a\(b>
    RegExpBranchImpl: <a\(b>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <\(>
        PsiElement(ESC_CHARACTER)('\(')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')