REGEXP_FILE
  RegExpPatternImpl: <abc>
    RegExpBranchImpl: <abc>
      RegExpCharImpl: <a>
        PsiElement(CHARACTER)('a')
      RegExpCharImpl: <b>
        PsiElement(CHARACTER)('b')
      RegExpCharImpl: <c>
        PsiElement(CHARACTER)('c')
  PsiErrorElement:Unmatched closing ')'
    <empty list>
  PsiElement(GROUP_END)(')')