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