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