REGEXP_FILE
  RegExpPatternImpl: <(.)=\1>
    RegExpBranchImpl: <(.)=\1>
      RegExpGroupImpl: <(.)>
        PsiElement(GROUP_BEGIN)('(')
        RegExpPatternImpl: <.>
          RegExpBranchImpl: <.>
            RegExpSimpleClassImpl: <.>
              PsiElement(DOT)('.')
        PsiElement(GROUP_END)(')')
      RegExpCharImpl: <=>
        PsiElement(CHARACTER)('=')
      RegExpBackrefImpl: <\1>
        PsiElement(BACKREF)('\1')