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