REGEXP_FILE
  RegExpPatternImpl: <(?:a)>
    RegExpBranchImpl: <(?:a)>
      RegExpGroupImpl: <(?:a)>
        PsiElement(NON_CAPT_GROUP)('(?:')
        RegExpPatternImpl: <a>
          RegExpBranchImpl: <a>
            RegExpCharImpl: <a>
              PsiElement(CHARACTER)('a')
        PsiElement(GROUP_END)(')')