REGEXP_FILE
  RegExpPatternImpl: <(?i|abc>
    RegExpBranchImpl: <(?i>
      RegExpSetOptionsImpl: <(?i>
        PsiElement(SET_OPTIONS)('(?')
        RegExpOptionsImpl: <i>
          PsiElement(OPTIONS_ON)('i')
        PsiErrorElement:Unclosed options group
          <empty list>
    PsiElement(UNION)('|')
    RegExpBranchImpl: <abc>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')