REGEXP_FILE
  RegExpPatternImpl: <>
    RegExpBranchImpl: <>
      <empty list>
  PsiErrorElement:Unmatched closing ')'
    <empty list>
  PsiElement(GROUP_END)(')')
  RegExpPatternImpl: <(>
    RegExpBranchImpl: <(>
      RegExpGroupImpl: <(>
        PsiElement(GROUP_BEGIN)('(')
        RegExpPatternImpl: <>
          RegExpBranchImpl: <>
            <empty list>
        PsiErrorElement:')' expected
          <empty list>